diff --git a/add_participant.py b/add_participant.py
new file mode 100644
index 0000000..fa4006f
--- /dev/null
+++ b/add_participant.py
@@ -0,0 +1,48 @@
+import asyncio
+from app.core.database import AsyncSessionLocal, Base, engine
+from app.models.ticket import Ticket
+from sqlalchemy import String, ForeignKey, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from app.core.database import GUID
+import uuid
+
+# Agregar modelo al archivo ticket.py
+new_model = '''
+
+class TicketParticipant(Base):
+    """Participantes asignados a un ticket"""
+    __tablename__ = "ticket_participants"
+
+    ticket_id: Mapped[uuid.UUID] = mapped_column(
+        GUID(),
+        ForeignKey("tickets.id", ondelete="CASCADE"),
+        nullable=False
+    )
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        GUID(),
+        ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False
+    )
+    role: Mapped[str] = mapped_column(String(50), nullable=False, default="participant")
+
+    ticket: Mapped["Ticket"] = relationship("Ticket", back_populates="participants")
+    user: Mapped["User"] = relationship("User")
+
+    __table_args__ = (
+        UniqueConstraint("ticket_id", "user_id", name="uq_ticket_participant"),
+    )
+
+    def __repr__(self):
+        return f"<TicketParticipant(ticket={self.ticket_id}, user={self.user_id})>"
+'''
+
+with open("/app/app/models/ticket.py", "r") as f:
+    content = f.read()
+
+if "TicketParticipant" in content:
+    print("Ya existe TicketParticipant")
+else:
+    content += new_model
+    with open("/app/app/models/ticket.py", "w") as f:
+        f.write(content)
+    print("OK: TicketParticipant agregado")
diff --git a/add_relation.py b/add_relation.py
new file mode 100644
index 0000000..aa184b3
--- /dev/null
+++ b/add_relation.py
@@ -0,0 +1,21 @@
+with open("/app/app/models/ticket.py", "r") as f:
+    content = f.read()
+
+old = '    def __repr__(self) -> str:\n        return f"<Ticket(id={self.id}, number=\'{self.ticket_number}\', status={self.status})>"'
+new = '''    participants: Mapped[list["TicketParticipant"]] = relationship(
+        "TicketParticipant",
+        back_populates="ticket",
+        cascade="all, delete-orphan"
+    )
+
+    def __repr__(self) -> str:
+        return f"<Ticket(id={self.id}, number=\'{self.ticket_number}\', status={self.status})>"'''
+
+if old in content:
+    content = content.replace(old, new)
+    print("OK: relacion participants agregada")
+else:
+    print("ERROR: bloque no encontrado")
+
+with open("/app/app/models/ticket.py", "w") as f:
+    f.write(content)
diff --git a/backend/add_participant.py b/backend/add_participant.py
new file mode 100644
index 0000000..fa4006f
--- /dev/null
+++ b/backend/add_participant.py
@@ -0,0 +1,48 @@
+import asyncio
+from app.core.database import AsyncSessionLocal, Base, engine
+from app.models.ticket import Ticket
+from sqlalchemy import String, ForeignKey, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from app.core.database import GUID
+import uuid
+
+# Agregar modelo al archivo ticket.py
+new_model = '''
+
+class TicketParticipant(Base):
+    """Participantes asignados a un ticket"""
+    __tablename__ = "ticket_participants"
+
+    ticket_id: Mapped[uuid.UUID] = mapped_column(
+        GUID(),
+        ForeignKey("tickets.id", ondelete="CASCADE"),
+        nullable=False
+    )
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        GUID(),
+        ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False
+    )
+    role: Mapped[str] = mapped_column(String(50), nullable=False, default="participant")
+
+    ticket: Mapped["Ticket"] = relationship("Ticket", back_populates="participants")
+    user: Mapped["User"] = relationship("User")
+
+    __table_args__ = (
+        UniqueConstraint("ticket_id", "user_id", name="uq_ticket_participant"),
+    )
+
+    def __repr__(self):
+        return f"<TicketParticipant(ticket={self.ticket_id}, user={self.user_id})>"
+'''
+
+with open("/app/app/models/ticket.py", "r") as f:
+    content = f.read()
+
+if "TicketParticipant" in content:
+    print("Ya existe TicketParticipant")
+else:
+    content += new_model
+    with open("/app/app/models/ticket.py", "w") as f:
+        f.write(content)
+    print("OK: TicketParticipant agregado")
diff --git a/backend/add_relation.py b/backend/add_relation.py
new file mode 100644
index 0000000..aa184b3
--- /dev/null
+++ b/backend/add_relation.py
@@ -0,0 +1,21 @@
+with open("/app/app/models/ticket.py", "r") as f:
+    content = f.read()
+
+old = '    def __repr__(self) -> str:\n        return f"<Ticket(id={self.id}, number=\'{self.ticket_number}\', status={self.status})>"'
+new = '''    participants: Mapped[list["TicketParticipant"]] = relationship(
+        "TicketParticipant",
+        back_populates="ticket",
+        cascade="all, delete-orphan"
+    )
+
+    def __repr__(self) -> str:
+        return f"<Ticket(id={self.id}, number=\'{self.ticket_number}\', status={self.status})>"'''
+
+if old in content:
+    content = content.replace(old, new)
+    print("OK: relacion participants agregada")
+else:
+    print("ERROR: bloque no encontrado")
+
+with open("/app/app/models/ticket.py", "w") as f:
+    f.write(content)
diff --git a/backend/app/api/schemas/category.py b/backend/app/api/schemas/category.py
index 91cda6d..3d33381 100644
--- a/backend/app/api/schemas/category.py
+++ b/backend/app/api/schemas/category.py
@@ -11,13 +11,14 @@ import uuid
 
 
 class CategoryCreate(BaseModel):
-    """Schema para crear categoría. No incluye tenant_id (se asigna automáticamente)."""
+    """Schema para crear categoría. tenant_id opcional para ADMIN global."""
     name: str
     description: Optional[str] = None
     color: Optional[str] = None
     sla_response_hours: int = 24
     sla_resolution_hours: int = 72
     auto_assign_to: Optional[uuid.UUID] = None
+    tenant_id: Optional[uuid.UUID] = None
 
 
 class CategoryUpdate(BaseModel):
diff --git a/backend/app/api/v1/endpoints/categories.py b/backend/app/api/v1/endpoints/categories.py
index 4376e03..6690ced 100644
--- a/backend/app/api/v1/endpoints/categories.py
+++ b/backend/app/api/v1/endpoints/categories.py
@@ -79,11 +79,16 @@ async def create_category(
     
     ✅ Implementa multi-tenancy: asigna automáticamente tenant_id del usuario.
     """
-    # ✅ CORREGIDO: Asignar tenant_id del usuario actual
-    db_category = Category(
-        **category.model_dump(),
-        tenant_id=current_user.tenant_id  # ✅ Multi-tenancy automático
-    )
+    # ADMIN global puede especificar tenant_id; otros usan el suyo
+    from app.models.user import UserRole as _R
+    data = category.model_dump()
+    if current_user.role == _R.ADMIN and data.get("tenant_id"):
+        target_tenant_id = data["tenant_id"]
+    else:
+        target_tenant_id = current_user.tenant_id
+        data["tenant_id"] = target_tenant_id
+
+    db_category = Category(**data)
     
     db.add(db_category)
     await db.commit()
diff --git a/backend/app/api/v1/endpoints/participants.py b/backend/app/api/v1/endpoints/participants.py
new file mode 100644
index 0000000..15376e9
--- /dev/null
+++ b/backend/app/api/v1/endpoints/participants.py
@@ -0,0 +1,130 @@
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select
+from sqlalchemy.orm import selectinload
+import uuid
+
+from app.api import deps
+from app.core.database import get_db
+from app.models.ticket import Ticket, TicketParticipant
+from app.models.user import User
+from pydantic import BaseModel
+
+router = APIRouter()
+
+class ParticipantAdd(BaseModel):
+    user_id: uuid.UUID
+
+class ParticipantResponse(BaseModel):
+    id: uuid.UUID
+    user_id: uuid.UUID
+    ticket_id: uuid.UUID
+    role: str
+    user_email: str
+    user_name: str
+
+    class Config:
+        from_attributes = True
+
+@router.get("/{ticket_id}/participants", response_model=list[ParticipantResponse])
+async def list_participants(
+    ticket_id: uuid.UUID,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(deps.get_current_user)
+):
+    result = await db.execute(
+        select(TicketParticipant)
+        .where(TicketParticipant.ticket_id == ticket_id)
+        .options(selectinload(TicketParticipant.user))
+    )
+    participants = result.scalars().all()
+    return [
+        ParticipantResponse(
+            id=p.id,
+            user_id=p.user_id,
+            ticket_id=p.ticket_id,
+            role=p.role,
+            user_email=p.user.email,
+            user_name=f"{p.user.first_name or ''} {p.user.last_name or ''}".strip()
+        )
+        for p in participants
+    ]
+
+@router.post("/{ticket_id}/participants", response_model=ParticipantResponse)
+async def add_participant(
+    ticket_id: uuid.UUID,
+    data: ParticipantAdd,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(deps.get_current_user)
+):
+    # Verificar que el ticket existe
+    ticket_result = await db.execute(select(Ticket).where(Ticket.id == ticket_id))
+    ticket = ticket_result.scalar_one_or_none()
+    if not ticket:
+        raise HTTPException(status_code=404, detail="Ticket not found")
+
+    # Solo el creador puede agregar participantes
+    if ticket.created_by != current_user.id and not current_user.role.is_global:
+        raise HTTPException(status_code=403, detail="Only the ticket creator can add participants")
+
+    # Verificar que el usuario existe
+    user_result = await db.execute(select(User).where(User.id == data.user_id))
+    user = user_result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    # Verificar que no sea duplicado
+    existing = await db.execute(
+        select(TicketParticipant).where(
+            TicketParticipant.ticket_id == ticket_id,
+            TicketParticipant.user_id == data.user_id
+        )
+    )
+    if existing.scalar_one_or_none():
+        raise HTTPException(status_code=400, detail="User is already a participant")
+
+    participant = TicketParticipant(
+        ticket_id=ticket_id,
+        user_id=data.user_id,
+        role="participant"
+    )
+    db.add(participant)
+    await db.commit()
+    await db.refresh(participant)
+
+    return ParticipantResponse(
+        id=participant.id,
+        user_id=participant.user_id,
+        ticket_id=participant.ticket_id,
+        role=participant.role,
+        user_email=user.email,
+        user_name=f"{user.first_name or ''} {user.last_name or ''}".strip()
+    )
+
+@router.delete("/{ticket_id}/participants/{user_id}", status_code=204)
+async def remove_participant(
+    ticket_id: uuid.UUID,
+    user_id: uuid.UUID,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(deps.get_current_user)
+):
+    ticket_result = await db.execute(select(Ticket).where(Ticket.id == ticket_id))
+    ticket = ticket_result.scalar_one_or_none()
+    if not ticket:
+        raise HTTPException(status_code=404, detail="Ticket not found")
+
+    if ticket.created_by != current_user.id and not current_user.role.is_global:
+        raise HTTPException(status_code=403, detail="Only the ticket creator can remove participants")
+
+    result = await db.execute(
+        select(TicketParticipant).where(
+            TicketParticipant.ticket_id == ticket_id,
+            TicketParticipant.user_id == user_id
+        )
+    )
+    participant = result.scalar_one_or_none()
+    if not participant:
+        raise HTTPException(status_code=404, detail="Participant not found")
+
+    await db.delete(participant)
+    await db.commit()
diff --git a/backend/app/api/v1/router.py b/backend/app/api/v1/router.py
index 1f491bf..56fd3e2 100644
--- a/backend/app/api/v1/router.py
+++ b/backend/app/api/v1/router.py
@@ -6,7 +6,7 @@ Router principal para la API v1
 
 from fastapi import APIRouter
 
-from app.api.v1.endpoints import auth, health, tenants, users, systems, categories, tickets, client_profile, audit, sla, reports
+from app.api.v1.endpoints import auth, health, tenants, users, systems, categories, tickets, client_profile, audit, sla, reports, participants
 
 api_router = APIRouter()
 
@@ -53,6 +53,12 @@ api_router.include_router(
     prefix="/tickets",
     tags=["tickets"]
 )
+# Participants routes (nested under tickets)
+api_router.include_router(
+    participants.router,
+    prefix="/tickets",
+    tags=["participants"]
+)
 
 # Client Profile routes
 api_router.include_router(
diff --git a/backend/app/models/ticket.py b/backend/app/models/ticket.py
index ab9b9ea..0ae54c2 100644
--- a/backend/app/models/ticket.py
+++ b/backend/app/models/ticket.py
@@ -157,5 +157,37 @@ class Ticket(Base):
         CheckConstraint('rating >= 1 AND rating <= 5', name='check_rating_range'),
     )
 
+    participants: Mapped[list["TicketParticipant"]] = relationship(
+        "TicketParticipant",
+        back_populates="ticket",
+        cascade="all, delete-orphan"
+    )
+
     def __repr__(self) -> str:
-        return f"<Ticket(id={self.id}, number='{self.ticket_number}', status={self.status})>"
\ No newline at end of file
+        return f"<Ticket(id={self.id}, number='{self.ticket_number}', status={self.status})>"
+
+class TicketParticipant(Base):
+    """Participantes asignados a un ticket"""
+    __tablename__ = "ticket_participants"
+
+    ticket_id: Mapped[uuid.UUID] = mapped_column(
+        GUID(),
+        ForeignKey("tickets.id", ondelete="CASCADE"),
+        nullable=False
+    )
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        GUID(),
+        ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False
+    )
+    role: Mapped[str] = mapped_column(String(50), nullable=False, default="participant")
+
+    ticket: Mapped["Ticket"] = relationship("Ticket", back_populates="participants")
+    user: Mapped["User"] = relationship("User")
+
+    __table_args__ = (
+        UniqueConstraint("ticket_id", "user_id", name="uq_ticket_participant"),
+    )
+
+    def __repr__(self):
+        return f"<TicketParticipant(ticket={self.ticket_id}, user={self.user_id})>"
diff --git a/backend/check_schema.py b/backend/check_schema.py
new file mode 100644
index 0000000..c638b34
--- /dev/null
+++ b/backend/check_schema.py
@@ -0,0 +1,3 @@
+with open("/app/app/api/schemas/category.py", "r") as f:
+    content = f.read()
+print(content)
diff --git a/backend/fix_categories.py b/backend/fix_categories.py
new file mode 100644
index 0000000..c45ad8a
--- /dev/null
+++ b/backend/fix_categories.py
@@ -0,0 +1,28 @@
+with open("/app/app/api/v1/endpoints/categories.py", "r") as f:
+    content = f.read()
+
+old = '''    # ✅ CORREGIDO: Asignar tenant_id del usuario actual
+    db_category = Category(
+        **category.model_dump(),
+        tenant_id=current_user.tenant_id  # ✅ Multi-tenancy automático
+    )'''
+
+new = '''    # ADMIN global puede especificar tenant_id; otros usan el suyo
+    from app.models.user import UserRole as _R
+    data = category.model_dump()
+    if current_user.role == _R.ADMIN and data.get("tenant_id"):
+        target_tenant_id = data["tenant_id"]
+    else:
+        target_tenant_id = current_user.tenant_id
+        data["tenant_id"] = target_tenant_id
+
+    db_category = Category(**data)'''
+
+if old in content:
+    content = content.replace(old, new)
+    print("OK: fix aplicado")
+else:
+    print("ERROR: bloque no encontrado")
+
+with open("/app/app/api/v1/endpoints/categories.py", "w") as f:
+    f.write(content)
diff --git a/backend/fix_router.py b/backend/fix_router.py
new file mode 100644
index 0000000..8e247fa
--- /dev/null
+++ b/backend/fix_router.py
@@ -0,0 +1,34 @@
+with open("/app/app/api/v1/router.py", "r") as f:
+    content = f.read()
+
+old = "from app.api.v1.endpoints import auth, health, tenants, users, systems, categories, tickets, client_profile, audit, sla, reports"
+new = "from app.api.v1.endpoints import auth, health, tenants, users, systems, categories, tickets, client_profile, audit, sla, reports, participants"
+
+old2 = "# Tickets routes\napi_router.include_router(\n    tickets.router,\n    prefix=\"/tickets\",\n    tags=[\"tickets\"]\n)"
+new2 = """# Tickets routes
+api_router.include_router(
+    tickets.router,
+    prefix="/tickets",
+    tags=["tickets"]
+)
+# Participants routes (nested under tickets)
+api_router.include_router(
+    participants.router,
+    prefix="/tickets",
+    tags=["participants"]
+)"""
+
+if old in content:
+    content = content.replace(old, new)
+    print("OK: import agregado")
+else:
+    print("ERROR: import no encontrado")
+
+if old2 in content:
+    content = content.replace(old2, new2)
+    print("OK: router agregado")
+else:
+    print("ERROR: router no encontrado")
+
+with open("/app/app/api/v1/router.py", "w") as f:
+    f.write(content)
diff --git a/backend/fix_schema.py b/backend/fix_schema.py
new file mode 100644
index 0000000..711afe6
--- /dev/null
+++ b/backend/fix_schema.py
@@ -0,0 +1,30 @@
+with open("/app/app/api/schemas/category.py", "r") as f:
+    content = f.read()
+
+old = '''class CategoryCreate(BaseModel):
+    """Schema para crear categoría. No incluye tenant_id (se asigna automáticamente)."""
+    name: str
+    description: Optional[str] = None
+    color: Optional[str] = None
+    sla_response_hours: int = 24
+    sla_resolution_hours: int = 72
+    auto_assign_to: Optional[uuid.UUID] = None'''
+
+new = '''class CategoryCreate(BaseModel):
+    """Schema para crear categoría. tenant_id opcional para ADMIN global."""
+    name: str
+    description: Optional[str] = None
+    color: Optional[str] = None
+    sla_response_hours: int = 24
+    sla_resolution_hours: int = 72
+    auto_assign_to: Optional[uuid.UUID] = None
+    tenant_id: Optional[uuid.UUID] = None'''
+
+if old in content:
+    content = content.replace(old, new)
+    print("OK")
+else:
+    print("ERROR: bloque no encontrado")
+
+with open("/app/app/api/schemas/category.py", "w") as f:
+    f.write(content)
diff --git a/backend/migrations/versions/46bccd948688_add_ticket_participants.py b/backend/migrations/versions/46bccd948688_add_ticket_participants.py
new file mode 100644
index 0000000..f01e7eb
--- /dev/null
+++ b/backend/migrations/versions/46bccd948688_add_ticket_participants.py
@@ -0,0 +1,28 @@
+"""add_ticket_participants
+
+Revision ID: 46bccd948688
+Revises: d2e3f4a5b6c7
+Create Date: 2026-03-11 17:59:55.409878
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = '46bccd948688'
+down_revision = 'd2e3f4a5b6c7'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    pass
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    pass
+    # ### end Alembic commands ###
\ No newline at end of file
diff --git a/check_schema.py b/check_schema.py
new file mode 100644
index 0000000..c638b34
--- /dev/null
+++ b/check_schema.py
@@ -0,0 +1,3 @@
+with open("/app/app/api/schemas/category.py", "r") as f:
+    content = f.read()
+print(content)
diff --git a/fix_categories.py b/fix_categories.py
new file mode 100644
index 0000000..c45ad8a
--- /dev/null
+++ b/fix_categories.py
@@ -0,0 +1,28 @@
+with open("/app/app/api/v1/endpoints/categories.py", "r") as f:
+    content = f.read()
+
+old = '''    # ✅ CORREGIDO: Asignar tenant_id del usuario actual
+    db_category = Category(
+        **category.model_dump(),
+        tenant_id=current_user.tenant_id  # ✅ Multi-tenancy automático
+    )'''
+
+new = '''    # ADMIN global puede especificar tenant_id; otros usan el suyo
+    from app.models.user import UserRole as _R
+    data = category.model_dump()
+    if current_user.role == _R.ADMIN and data.get("tenant_id"):
+        target_tenant_id = data["tenant_id"]
+    else:
+        target_tenant_id = current_user.tenant_id
+        data["tenant_id"] = target_tenant_id
+
+    db_category = Category(**data)'''
+
+if old in content:
+    content = content.replace(old, new)
+    print("OK: fix aplicado")
+else:
+    print("ERROR: bloque no encontrado")
+
+with open("/app/app/api/v1/endpoints/categories.py", "w") as f:
+    f.write(content)
diff --git a/fix_router.py b/fix_router.py
new file mode 100644
index 0000000..8e247fa
--- /dev/null
+++ b/fix_router.py
@@ -0,0 +1,34 @@
+with open("/app/app/api/v1/router.py", "r") as f:
+    content = f.read()
+
+old = "from app.api.v1.endpoints import auth, health, tenants, users, systems, categories, tickets, client_profile, audit, sla, reports"
+new = "from app.api.v1.endpoints import auth, health, tenants, users, systems, categories, tickets, client_profile, audit, sla, reports, participants"
+
+old2 = "# Tickets routes\napi_router.include_router(\n    tickets.router,\n    prefix=\"/tickets\",\n    tags=[\"tickets\"]\n)"
+new2 = """# Tickets routes
+api_router.include_router(
+    tickets.router,
+    prefix="/tickets",
+    tags=["tickets"]
+)
+# Participants routes (nested under tickets)
+api_router.include_router(
+    participants.router,
+    prefix="/tickets",
+    tags=["participants"]
+)"""
+
+if old in content:
+    content = content.replace(old, new)
+    print("OK: import agregado")
+else:
+    print("ERROR: import no encontrado")
+
+if old2 in content:
+    content = content.replace(old2, new2)
+    print("OK: router agregado")
+else:
+    print("ERROR: router no encontrado")
+
+with open("/app/app/api/v1/router.py", "w") as f:
+    f.write(content)
diff --git a/fix_schema.py b/fix_schema.py
new file mode 100644
index 0000000..711afe6
--- /dev/null
+++ b/fix_schema.py
@@ -0,0 +1,30 @@
+with open("/app/app/api/schemas/category.py", "r") as f:
+    content = f.read()
+
+old = '''class CategoryCreate(BaseModel):
+    """Schema para crear categoría. No incluye tenant_id (se asigna automáticamente)."""
+    name: str
+    description: Optional[str] = None
+    color: Optional[str] = None
+    sla_response_hours: int = 24
+    sla_resolution_hours: int = 72
+    auto_assign_to: Optional[uuid.UUID] = None'''
+
+new = '''class CategoryCreate(BaseModel):
+    """Schema para crear categoría. tenant_id opcional para ADMIN global."""
+    name: str
+    description: Optional[str] = None
+    color: Optional[str] = None
+    sla_response_hours: int = 24
+    sla_resolution_hours: int = 72
+    auto_assign_to: Optional[uuid.UUID] = None
+    tenant_id: Optional[uuid.UUID] = None'''
+
+if old in content:
+    content = content.replace(old, new)
+    print("OK")
+else:
+    print("ERROR: bloque no encontrado")
+
+with open("/app/app/api/schemas/category.py", "w") as f:
+    f.write(content)
diff --git a/frontend-client/src/lib/components/ParticipantsModal.svelte b/frontend-client/src/lib/components/ParticipantsModal.svelte
new file mode 100644
index 0000000..aa1def8
--- /dev/null
+++ b/frontend-client/src/lib/components/ParticipantsModal.svelte
@@ -0,0 +1,242 @@
+<script lang="ts">
+  import { createEventDispatcher, onMount } from 'svelte';
+  import { api } from '$lib/utils/api';
+  import { toast } from '$lib/stores/toast';
+  import { auth } from '$lib/stores/auth';
+
+  export let ticketId: string;
+  export let createdBy: string;
+
+  const dispatch = createEventDispatcher();
+
+  interface Participant {
+    id: string;
+    user_id: string;
+    ticket_id: string;
+    role: string;
+    user_email: string;
+    user_name: string;
+  }
+
+  interface User {
+    id: string;
+    email: string;
+    first_name: string;
+    last_name: string;
+    role: string;
+  }
+
+  let participants: Participant[] = [];
+  let allUsers: User[] = [];
+  let isLoading = true;
+  let isAdding = false;
+  let searchQuery = '';
+  let selectedUserId = '';
+
+  $: isCreator = $auth.user?.id === createdBy;
+  $: isGlobalAdmin = $auth.user?.role === 'ADMIN';
+  $: canManage = isCreator || isGlobalAdmin;
+
+  $: participantIds = new Set(participants.map(p => p.user_id));
+
+  $: filteredUsers = allUsers.filter(u => {
+    if (participantIds.has(u.id)) return false;
+    if (u.id === createdBy) return false;
+    const q = searchQuery.toLowerCase();
+    return !q ||
+      u.email.toLowerCase().includes(q) ||
+      `${u.first_name} ${u.last_name}`.toLowerCase().includes(q);
+  });
+
+  onMount(async () => {
+    await Promise.all([loadParticipants(), loadUsers()]);
+    isLoading = false;
+  });
+
+  async function loadParticipants() {
+    try {
+      participants = await api.get(`/tickets/${ticketId}/participants`);
+    } catch (e: any) {
+      toast.error('Error cargando participantes');
+    }
+  }
+
+  async function loadUsers() {
+    try {
+      allUsers = await api.get('/users/');
+    } catch (e: any) {
+      toast.error('Error cargando usuarios');
+    }
+  }
+
+  async function addParticipant(userId: string) {
+    if (!userId) return;
+    isAdding = true;
+    try {
+      const p = await api.post(`/tickets/${ticketId}/participants`, { user_id: userId });
+      participants = [...participants, p];
+      searchQuery = '';
+      toast.success('Participante agregado');
+    } catch (e: any) {
+      toast.error(e.message || 'Error al agregar participante');
+    } finally {
+      isAdding = false;
+    }
+  }
+
+  async function removeParticipant(userId: string) {
+    try {
+      await api.delete(`/tickets/${ticketId}/participants/${userId}`);
+      participants = participants.filter(p => p.user_id !== userId);
+      toast.success('Participante eliminado');
+    } catch (e: any) {
+      toast.error(e.message || 'Error al eliminar participante');
+    }
+  }
+
+  function avatarInitials(name: string, email: string): string {
+    if (name.trim()) {
+      const parts = name.trim().split(' ');
+      return (parts[0][0] + (parts[1]?.[0] || '')).toUpperCase();
+    }
+    return email[0].toUpperCase();
+  }
+
+  function avatarColor(email: string): string {
+    const colors = ['bg-blue-400', 'bg-violet-400', 'bg-emerald-400', 'bg-rose-400', 'bg-amber-400', 'bg-cyan-400'];
+    let hash = 0;
+    for (const c of email) hash = (hash << 5) - hash + c.charCodeAt(0);
+    return colors[Math.abs(hash) % colors.length];
+  }
+</script>
+
+<!-- Overlay -->
+<div class="fixed inset-0 z-50 flex items-center justify-center p-4">
+  <div class="absolute inset-0 bg-black/40 backdrop-blur-sm" on:click={() => dispatch('close')}></div>
+
+  <div class="relative bg-white rounded-2xl shadow-2xl w-full max-w-lg z-10 overflow-hidden">
+
+    <!-- Header -->
+    <div class="flex items-center justify-between px-6 py-4 border-b border-gray-100">
+      <div>
+        <h2 class="text-lg font-semibold text-gray-900">Participantes del asunto</h2>
+        <p class="text-xs text-gray-400 mt-0.5">{participants.length} persona{participants.length !== 1 ? 's' : ''} involucrada{participants.length !== 1 ? 's' : ''}</p>
+      </div>
+      <button type="button" on:click={() => dispatch('close')}
+        class="p-1.5 rounded-lg hover:bg-gray-100 text-gray-400 transition-colors">
+        <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
+        </svg>
+      </button>
+    </div>
+
+    <div class="p-6 space-y-5 max-h-[70vh] overflow-y-auto">
+
+      <!-- Buscador para agregar -->
+      {#if canManage}
+        <div>
+          <label class="block text-sm font-medium text-gray-700 mb-2">Agregar persona</label>
+          <div class="relative">
+            <svg class="absolute left-3 top-1/2 -translate-y-1/2 w-4 h-4 text-gray-400" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z"/>
+            </svg>
+            <input
+              type="text"
+              placeholder="Buscar por nombre o email..."
+              bind:value={searchQuery}
+              class="w-full pl-9 pr-4 py-2 text-sm border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500"
+            />
+          </div>
+
+          <!-- Resultados de búsqueda -->
+          {#if searchQuery && filteredUsers.length > 0}
+            <div class="mt-2 border border-gray-200 rounded-lg overflow-hidden shadow-sm">
+              {#each filteredUsers.slice(0, 6) as user (user.id)}
+                <button
+                  type="button"
+                  on:click={() => addParticipant(user.id)}
+                  disabled={isAdding}
+                  class="w-full flex items-center gap-3 px-4 py-3 hover:bg-blue-50 transition-colors text-left border-b border-gray-100 last:border-0"
+                >
+                  <div class="w-8 h-8 rounded-full {avatarColor(user.email)} flex items-center justify-center text-white text-xs font-bold flex-shrink-0">
+                    {avatarInitials(`${user.first_name} ${user.last_name}`, user.email)}
+                  </div>
+                  <div class="min-w-0">
+                    <p class="text-sm font-medium text-gray-900 truncate">{user.first_name} {user.last_name}</p>
+                    <p class="text-xs text-gray-400 truncate">{user.email}</p>
+                  </div>
+                  <span class="ml-auto text-xs text-blue-600 font-medium flex-shrink-0">+ Agregar</span>
+                </button>
+              {/each}
+            </div>
+          {:else if searchQuery && filteredUsers.length === 0}
+            <p class="mt-2 text-sm text-gray-400 text-center py-2">No se encontraron usuarios disponibles</p>
+          {/if}
+        </div>
+      {/if}
+
+      <!-- Lista de participantes -->
+      <div>
+        <h3 class="text-sm font-medium text-gray-700 mb-3">
+          {canManage ? 'Participantes actuales' : 'Personas involucradas'}
+        </h3>
+
+        {#if isLoading}
+          <div class="flex justify-center py-6">
+            <div class="animate-spin rounded-full h-6 w-6 border-b-2 border-blue-600"></div>
+          </div>
+
+        {:else if participants.length === 0}
+          <div class="text-center py-8 bg-gray-50 rounded-lg border border-dashed border-gray-200">
+            <svg class="w-10 h-10 mx-auto text-gray-300 mb-2" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="1.5" d="M17 20h5v-2a3 3 0 00-5.356-1.857M17 20H7m10 0v-2c0-.656-.126-1.283-.356-1.857M7 20H2v-2a3 3 0 015.356-1.857M7 20v-2c0-.656.126-1.283.356-1.857m0 0a5.002 5.002 0 019.288 0M15 7a3 3 0 11-6 0 3 3 0 016 0z"/>
+            </svg>
+            <p class="text-sm text-gray-400">Aún no hay participantes</p>
+            {#if canManage}
+              <p class="text-xs text-gray-300 mt-1">Usa el buscador para agregar personas</p>
+            {/if}
+          </div>
+
+        {:else}
+          <div class="space-y-2">
+            {#each participants as p (p.id)}
+              <div class="flex items-center gap-3 p-3 bg-gray-50 rounded-lg group">
+                <div class="w-9 h-9 rounded-full {avatarColor(p.user_email)} flex items-center justify-center text-white text-xs font-bold flex-shrink-0">
+                  {avatarInitials(p.user_name, p.user_email)}
+                </div>
+                <div class="min-w-0 flex-1">
+                  <p class="text-sm font-medium text-gray-900 truncate">{p.user_name || p.user_email}</p>
+                  <p class="text-xs text-gray-400 truncate">{p.user_email}</p>
+                </div>
+                <span class="text-xs text-gray-400 bg-white px-2 py-0.5 rounded-full border border-gray-200">
+                  Participante
+                </span>
+                {#if canManage}
+                  <button
+                    type="button"
+                    on:click={() => removeParticipant(p.user_id)}
+                    class="p-1 rounded text-gray-300 hover:text-rose-500 hover:bg-rose-50 transition-colors opacity-0 group-hover:opacity-100"
+                    title="Quitar participante"
+                  >
+                    <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                      <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
+                    </svg>
+                  </button>
+                {/if}
+              </div>
+            {/each}
+          </div>
+        {/if}
+      </div>
+    </div>
+
+    <!-- Footer -->
+    <div class="px-6 py-4 bg-gray-50 border-t border-gray-100 flex justify-end">
+      <button type="button" on:click={() => dispatch('close')}
+        class="px-4 py-2 text-sm font-medium text-gray-700 bg-white border border-gray-200 rounded-lg hover:bg-gray-50 transition-colors">
+        Cerrar
+      </button>
+    </div>
+
+  </div>
+</div>
diff --git a/frontend-internal/src/lib/components/ParticipantsModal.svelte b/frontend-internal/src/lib/components/ParticipantsModal.svelte
new file mode 100644
index 0000000..aa1def8
--- /dev/null
+++ b/frontend-internal/src/lib/components/ParticipantsModal.svelte
@@ -0,0 +1,242 @@
+<script lang="ts">
+  import { createEventDispatcher, onMount } from 'svelte';
+  import { api } from '$lib/utils/api';
+  import { toast } from '$lib/stores/toast';
+  import { auth } from '$lib/stores/auth';
+
+  export let ticketId: string;
+  export let createdBy: string;
+
+  const dispatch = createEventDispatcher();
+
+  interface Participant {
+    id: string;
+    user_id: string;
+    ticket_id: string;
+    role: string;
+    user_email: string;
+    user_name: string;
+  }
+
+  interface User {
+    id: string;
+    email: string;
+    first_name: string;
+    last_name: string;
+    role: string;
+  }
+
+  let participants: Participant[] = [];
+  let allUsers: User[] = [];
+  let isLoading = true;
+  let isAdding = false;
+  let searchQuery = '';
+  let selectedUserId = '';
+
+  $: isCreator = $auth.user?.id === createdBy;
+  $: isGlobalAdmin = $auth.user?.role === 'ADMIN';
+  $: canManage = isCreator || isGlobalAdmin;
+
+  $: participantIds = new Set(participants.map(p => p.user_id));
+
+  $: filteredUsers = allUsers.filter(u => {
+    if (participantIds.has(u.id)) return false;
+    if (u.id === createdBy) return false;
+    const q = searchQuery.toLowerCase();
+    return !q ||
+      u.email.toLowerCase().includes(q) ||
+      `${u.first_name} ${u.last_name}`.toLowerCase().includes(q);
+  });
+
+  onMount(async () => {
+    await Promise.all([loadParticipants(), loadUsers()]);
+    isLoading = false;
+  });
+
+  async function loadParticipants() {
+    try {
+      participants = await api.get(`/tickets/${ticketId}/participants`);
+    } catch (e: any) {
+      toast.error('Error cargando participantes');
+    }
+  }
+
+  async function loadUsers() {
+    try {
+      allUsers = await api.get('/users/');
+    } catch (e: any) {
+      toast.error('Error cargando usuarios');
+    }
+  }
+
+  async function addParticipant(userId: string) {
+    if (!userId) return;
+    isAdding = true;
+    try {
+      const p = await api.post(`/tickets/${ticketId}/participants`, { user_id: userId });
+      participants = [...participants, p];
+      searchQuery = '';
+      toast.success('Participante agregado');
+    } catch (e: any) {
+      toast.error(e.message || 'Error al agregar participante');
+    } finally {
+      isAdding = false;
+    }
+  }
+
+  async function removeParticipant(userId: string) {
+    try {
+      await api.delete(`/tickets/${ticketId}/participants/${userId}`);
+      participants = participants.filter(p => p.user_id !== userId);
+      toast.success('Participante eliminado');
+    } catch (e: any) {
+      toast.error(e.message || 'Error al eliminar participante');
+    }
+  }
+
+  function avatarInitials(name: string, email: string): string {
+    if (name.trim()) {
+      const parts = name.trim().split(' ');
+      return (parts[0][0] + (parts[1]?.[0] || '')).toUpperCase();
+    }
+    return email[0].toUpperCase();
+  }
+
+  function avatarColor(email: string): string {
+    const colors = ['bg-blue-400', 'bg-violet-400', 'bg-emerald-400', 'bg-rose-400', 'bg-amber-400', 'bg-cyan-400'];
+    let hash = 0;
+    for (const c of email) hash = (hash << 5) - hash + c.charCodeAt(0);
+    return colors[Math.abs(hash) % colors.length];
+  }
+</script>
+
+<!-- Overlay -->
+<div class="fixed inset-0 z-50 flex items-center justify-center p-4">
+  <div class="absolute inset-0 bg-black/40 backdrop-blur-sm" on:click={() => dispatch('close')}></div>
+
+  <div class="relative bg-white rounded-2xl shadow-2xl w-full max-w-lg z-10 overflow-hidden">
+
+    <!-- Header -->
+    <div class="flex items-center justify-between px-6 py-4 border-b border-gray-100">
+      <div>
+        <h2 class="text-lg font-semibold text-gray-900">Participantes del asunto</h2>
+        <p class="text-xs text-gray-400 mt-0.5">{participants.length} persona{participants.length !== 1 ? 's' : ''} involucrada{participants.length !== 1 ? 's' : ''}</p>
+      </div>
+      <button type="button" on:click={() => dispatch('close')}
+        class="p-1.5 rounded-lg hover:bg-gray-100 text-gray-400 transition-colors">
+        <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
+        </svg>
+      </button>
+    </div>
+
+    <div class="p-6 space-y-5 max-h-[70vh] overflow-y-auto">
+
+      <!-- Buscador para agregar -->
+      {#if canManage}
+        <div>
+          <label class="block text-sm font-medium text-gray-700 mb-2">Agregar persona</label>
+          <div class="relative">
+            <svg class="absolute left-3 top-1/2 -translate-y-1/2 w-4 h-4 text-gray-400" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z"/>
+            </svg>
+            <input
+              type="text"
+              placeholder="Buscar por nombre o email..."
+              bind:value={searchQuery}
+              class="w-full pl-9 pr-4 py-2 text-sm border border-gray-200 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500"
+            />
+          </div>
+
+          <!-- Resultados de búsqueda -->
+          {#if searchQuery && filteredUsers.length > 0}
+            <div class="mt-2 border border-gray-200 rounded-lg overflow-hidden shadow-sm">
+              {#each filteredUsers.slice(0, 6) as user (user.id)}
+                <button
+                  type="button"
+                  on:click={() => addParticipant(user.id)}
+                  disabled={isAdding}
+                  class="w-full flex items-center gap-3 px-4 py-3 hover:bg-blue-50 transition-colors text-left border-b border-gray-100 last:border-0"
+                >
+                  <div class="w-8 h-8 rounded-full {avatarColor(user.email)} flex items-center justify-center text-white text-xs font-bold flex-shrink-0">
+                    {avatarInitials(`${user.first_name} ${user.last_name}`, user.email)}
+                  </div>
+                  <div class="min-w-0">
+                    <p class="text-sm font-medium text-gray-900 truncate">{user.first_name} {user.last_name}</p>
+                    <p class="text-xs text-gray-400 truncate">{user.email}</p>
+                  </div>
+                  <span class="ml-auto text-xs text-blue-600 font-medium flex-shrink-0">+ Agregar</span>
+                </button>
+              {/each}
+            </div>
+          {:else if searchQuery && filteredUsers.length === 0}
+            <p class="mt-2 text-sm text-gray-400 text-center py-2">No se encontraron usuarios disponibles</p>
+          {/if}
+        </div>
+      {/if}
+
+      <!-- Lista de participantes -->
+      <div>
+        <h3 class="text-sm font-medium text-gray-700 mb-3">
+          {canManage ? 'Participantes actuales' : 'Personas involucradas'}
+        </h3>
+
+        {#if isLoading}
+          <div class="flex justify-center py-6">
+            <div class="animate-spin rounded-full h-6 w-6 border-b-2 border-blue-600"></div>
+          </div>
+
+        {:else if participants.length === 0}
+          <div class="text-center py-8 bg-gray-50 rounded-lg border border-dashed border-gray-200">
+            <svg class="w-10 h-10 mx-auto text-gray-300 mb-2" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="1.5" d="M17 20h5v-2a3 3 0 00-5.356-1.857M17 20H7m10 0v-2c0-.656-.126-1.283-.356-1.857M7 20H2v-2a3 3 0 015.356-1.857M7 20v-2c0-.656.126-1.283.356-1.857m0 0a5.002 5.002 0 019.288 0M15 7a3 3 0 11-6 0 3 3 0 016 0z"/>
+            </svg>
+            <p class="text-sm text-gray-400">Aún no hay participantes</p>
+            {#if canManage}
+              <p class="text-xs text-gray-300 mt-1">Usa el buscador para agregar personas</p>
+            {/if}
+          </div>
+
+        {:else}
+          <div class="space-y-2">
+            {#each participants as p (p.id)}
+              <div class="flex items-center gap-3 p-3 bg-gray-50 rounded-lg group">
+                <div class="w-9 h-9 rounded-full {avatarColor(p.user_email)} flex items-center justify-center text-white text-xs font-bold flex-shrink-0">
+                  {avatarInitials(p.user_name, p.user_email)}
+                </div>
+                <div class="min-w-0 flex-1">
+                  <p class="text-sm font-medium text-gray-900 truncate">{p.user_name || p.user_email}</p>
+                  <p class="text-xs text-gray-400 truncate">{p.user_email}</p>
+                </div>
+                <span class="text-xs text-gray-400 bg-white px-2 py-0.5 rounded-full border border-gray-200">
+                  Participante
+                </span>
+                {#if canManage}
+                  <button
+                    type="button"
+                    on:click={() => removeParticipant(p.user_id)}
+                    class="p-1 rounded text-gray-300 hover:text-rose-500 hover:bg-rose-50 transition-colors opacity-0 group-hover:opacity-100"
+                    title="Quitar participante"
+                  >
+                    <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                      <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
+                    </svg>
+                  </button>
+                {/if}
+              </div>
+            {/each}
+          </div>
+        {/if}
+      </div>
+    </div>
+
+    <!-- Footer -->
+    <div class="px-6 py-4 bg-gray-50 border-t border-gray-100 flex justify-end">
+      <button type="button" on:click={() => dispatch('close')}
+        class="px-4 py-2 text-sm font-medium text-gray-700 bg-white border border-gray-200 rounded-lg hover:bg-gray-50 transition-colors">
+        Cerrar
+      </button>
+    </div>
+
+  </div>
+</div>
diff --git a/frontend-internal/src/routes/tickets/[id]/+page.svelte b/frontend-internal/src/routes/tickets/[id]/+page.svelte
index 02d685d..7c3bf9d 100644
--- a/frontend-internal/src/routes/tickets/[id]/+page.svelte
+++ b/frontend-internal/src/routes/tickets/[id]/+page.svelte
@@ -4,7 +4,9 @@
   import { toast } from '$lib/stores/toast';
   import { api } from '$lib/utils/api';
   import { onMount } from 'svelte';
+  import ParticipantsModal from '$lib/components/ParticipantsModal.svelte';
 
+  let showParticipants = false;
   let ticketId: string;
   let ticket = null;
   let comments = [];
@@ -374,6 +376,17 @@
               <dd class="text-sm text-gray-900">{formatDate(ticket.updated_at)}</dd>
             </div>
 
+            <!-- Participantes -->
+            <div class="bg-white shadow rounded-lg">
+            <div class="px-6 py-5 border-b border-gray-200 flex justify-between items-center">
+              <h3 class="text-lg font-semibold text-gray-900">Asunto</h3>
+            <button type="button" on:click={() => showParticipants = true}
+                    class="text-sm text-blue-600 hover:text-blue-700 font-medium">
+                  Gestionar
+            </button>
+          </div>
+          </div>
+
             <!-- SLA Information -->
             {#if ticket.sla_response_due || ticket.sla_resolution_due}
               <div class="pt-4 border-t border-gray-200">
@@ -429,4 +442,11 @@
       </div>
     </div>
   {/if}
+  {#if showParticipants && ticket}
+  <ParticipantsModal
+    ticketId={ticket.id}
+    createdBy={ticket.created_by}
+    on:close={() => showParticipants = false}
+  />
+{/if}
 </div>
diff --git a/participants_router.py b/participants_router.py
new file mode 100644
index 0000000..15376e9
--- /dev/null
+++ b/participants_router.py
@@ -0,0 +1,130 @@
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select
+from sqlalchemy.orm import selectinload
+import uuid
+
+from app.api import deps
+from app.core.database import get_db
+from app.models.ticket import Ticket, TicketParticipant
+from app.models.user import User
+from pydantic import BaseModel
+
+router = APIRouter()
+
+class ParticipantAdd(BaseModel):
+    user_id: uuid.UUID
+
+class ParticipantResponse(BaseModel):
+    id: uuid.UUID
+    user_id: uuid.UUID
+    ticket_id: uuid.UUID
+    role: str
+    user_email: str
+    user_name: str
+
+    class Config:
+        from_attributes = True
+
+@router.get("/{ticket_id}/participants", response_model=list[ParticipantResponse])
+async def list_participants(
+    ticket_id: uuid.UUID,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(deps.get_current_user)
+):
+    result = await db.execute(
+        select(TicketParticipant)
+        .where(TicketParticipant.ticket_id == ticket_id)
+        .options(selectinload(TicketParticipant.user))
+    )
+    participants = result.scalars().all()
+    return [
+        ParticipantResponse(
+            id=p.id,
+            user_id=p.user_id,
+            ticket_id=p.ticket_id,
+            role=p.role,
+            user_email=p.user.email,
+            user_name=f"{p.user.first_name or ''} {p.user.last_name or ''}".strip()
+        )
+        for p in participants
+    ]
+
+@router.post("/{ticket_id}/participants", response_model=ParticipantResponse)
+async def add_participant(
+    ticket_id: uuid.UUID,
+    data: ParticipantAdd,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(deps.get_current_user)
+):
+    # Verificar que el ticket existe
+    ticket_result = await db.execute(select(Ticket).where(Ticket.id == ticket_id))
+    ticket = ticket_result.scalar_one_or_none()
+    if not ticket:
+        raise HTTPException(status_code=404, detail="Ticket not found")
+
+    # Solo el creador puede agregar participantes
+    if ticket.created_by != current_user.id and not current_user.role.is_global:
+        raise HTTPException(status_code=403, detail="Only the ticket creator can add participants")
+
+    # Verificar que el usuario existe
+    user_result = await db.execute(select(User).where(User.id == data.user_id))
+    user = user_result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    # Verificar que no sea duplicado
+    existing = await db.execute(
+        select(TicketParticipant).where(
+            TicketParticipant.ticket_id == ticket_id,
+            TicketParticipant.user_id == data.user_id
+        )
+    )
+    if existing.scalar_one_or_none():
+        raise HTTPException(status_code=400, detail="User is already a participant")
+
+    participant = TicketParticipant(
+        ticket_id=ticket_id,
+        user_id=data.user_id,
+        role="participant"
+    )
+    db.add(participant)
+    await db.commit()
+    await db.refresh(participant)
+
+    return ParticipantResponse(
+        id=participant.id,
+        user_id=participant.user_id,
+        ticket_id=participant.ticket_id,
+        role=participant.role,
+        user_email=user.email,
+        user_name=f"{user.first_name or ''} {user.last_name or ''}".strip()
+    )
+
+@router.delete("/{ticket_id}/participants/{user_id}", status_code=204)
+async def remove_participant(
+    ticket_id: uuid.UUID,
+    user_id: uuid.UUID,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(deps.get_current_user)
+):
+    ticket_result = await db.execute(select(Ticket).where(Ticket.id == ticket_id))
+    ticket = ticket_result.scalar_one_or_none()
+    if not ticket:
+        raise HTTPException(status_code=404, detail="Ticket not found")
+
+    if ticket.created_by != current_user.id and not current_user.role.is_global:
+        raise HTTPException(status_code=403, detail="Only the ticket creator can remove participants")
+
+    result = await db.execute(
+        select(TicketParticipant).where(
+            TicketParticipant.ticket_id == ticket_id,
+            TicketParticipant.user_id == user_id
+        )
+    )
+    participant = result.scalar_one_or_none()
+    if not participant:
+        raise HTTPException(status_code=404, detail="Participant not found")
+
+    await db.delete(participant)
+    await db.commit()