diff --git a/backend/app/models/tenant.py b/backend/app/models/tenant.py
new file mode 100644
index 0000000..0b7a44c
--- /dev/null
+++ b/backend/app/models/tenant.py
@@ -0,0 +1,23 @@
+"""Tenant model - top-level isolation boundary."""
+from sqlalchemy import Column, String, Boolean, Text, Integer
+from app.models.base import Base, TimestampMixin
+
+
+class Tenant(Base, TimestampMixin):
+    """A tenant represents an organization / department.
+
+    All data (users, projects, tasks, workers) is isolated by tenant_id.
+    """
+    __tablename__ = "tenants"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    name = Column(String(200), nullable=False)
+    slug = Column(String(100), nullable=False, unique=True, index=True)
+    description = Column(Text, default="")
+    is_active = Column(Boolean, default=True, nullable=False)
+
+    # Tenant-level settings stored as JSON string
+    settings = Column(Text, default="{}")
+
+    def __repr__(self):
+        return f"<Tenant {self.slug}>"