diff --git a/backend/alembic/versions/073_add_device_types_table.py b/backend/alembic/versions/073_add_device_types_table.py
new file mode 100644
index 00000000..fb1b86e0
--- /dev/null
+++ b/backend/alembic/versions/073_add_device_types_table.py
@@ -0,0 +1,95 @@
+"""Add device_types table with system seed data.
+
+Revision ID: 073
+Revises: 072
+Create Date: 2026-04-04
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID
+import uuid
+
+
+revision = "073"
+down_revision = "072"
+branch_labels = None
+depends_on = None
+
+SYSTEM_DEVICE_TYPES = [
+    ("router", "Router", "network", 0),
+    ("switch", "Switch", "network", 1),
+    ("firewall", "Firewall", "network", 2),
+    ("access-point", "Access Point", "network", 3),
+    ("load-balancer", "Load Balancer", "network", 4),
+    ("server", "Server", "compute", 0),
+    ("workstation", "Workstation", "compute", 1),
+    ("vm", "Virtual Machine", "compute", 2),
+    ("container", "Container", "compute", 3),
+    ("nas", "NAS", "storage", 0),
+    ("san", "SAN", "storage", 1),
+    ("cloud-storage", "Cloud Storage", "storage", 2),
+    ("cloud", "Cloud", "cloud", 0),
+    ("aws", "AWS", "cloud", 1),
+    ("azure", "Azure", "cloud", 2),
+    ("gcp", "Google Cloud", "cloud", 3),
+    ("printer", "Printer", "endpoint", 0),
+    ("phone", "Phone", "endpoint", 1),
+    ("iot", "IoT Device", "endpoint", 2),
+    ("camera", "Camera", "endpoint", 3),
+    ("tablet", "Tablet", "endpoint", 4),
+    ("laptop", "Laptop", "endpoint", 5),
+    ("ups", "UPS", "infrastructure", 0),
+    ("pdu", "PDU", "infrastructure", 1),
+    ("rack", "Rack", "infrastructure", 2),
+    ("patch-panel", "Patch Panel", "infrastructure", 3),
+    ("nvr", "NVR", "security", 0),
+    ("badge-reader", "Badge Reader", "security", 1),
+]
+
+
+def upgrade() -> None:
+    op.create_table(
+        "device_types",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True, server_default=sa.text("gen_random_uuid()")),
+        sa.Column("slug", sa.String(50), nullable=False),
+        sa.Column("label", sa.String(100), nullable=False),
+        sa.Column("category", sa.String(50), nullable=False),
+        sa.Column("is_system", sa.Boolean(), nullable=False, server_default=sa.text("false")),
+        sa.Column("team_id", UUID(as_uuid=True), sa.ForeignKey("teams.id", ondelete="CASCADE"), nullable=True),
+        sa.Column("sort_order", sa.Integer(), nullable=False, server_default=sa.text("0")),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.text("now()")),
+    )
+
+    op.execute(
+        "ALTER TABLE device_types ADD CONSTRAINT uq_device_types_slug_team "
+        "UNIQUE NULLS NOT DISTINCT (slug, team_id)"
+    )
+    op.create_index("idx_device_types_team", "device_types", ["team_id"])
+
+    device_types_table = sa.table(
+        "device_types",
+        sa.column("id", UUID(as_uuid=True)),
+        sa.column("slug", sa.String),
+        sa.column("label", sa.String),
+        sa.column("category", sa.String),
+        sa.column("is_system", sa.Boolean),
+        sa.column("team_id", UUID(as_uuid=True)),
+        sa.column("sort_order", sa.Integer),
+    )
+
+    op.bulk_insert(device_types_table, [
+        {
+            "id": uuid.uuid4(),
+            "slug": slug,
+            "label": label,
+            "category": category,
+            "is_system": True,
+            "team_id": None,
+            "sort_order": sort_order,
+        }
+        for slug, label, category, sort_order in SYSTEM_DEVICE_TYPES
+    ])
+
+
+def downgrade() -> None:
+    op.drop_table("device_types")
diff --git a/backend/app/models/__init__.py b/backend/app/models/__init__.py
index 0441624f..895e82be 100644
--- a/backend/app/models/__init__.py
+++ b/backend/app/models/__init__.py
@@ -56,6 +56,7 @@ from .session_handoff import SessionHandoff
 from .session_resolution_output import SessionResolutionOutput
 from .template_tree import TemplateTree
 from .platform_step import PlatformStep
+from .device_type import DeviceType
 
 __all__ = [
     "User",
@@ -126,4 +127,5 @@ __all__ = [
     "SessionResolutionOutput",
     "TemplateTree",
     "PlatformStep",
+    "DeviceType",
 ]
diff --git a/backend/app/models/device_type.py b/backend/app/models/device_type.py
new file mode 100644
index 00000000..cb419cfb
--- /dev/null
+++ b/backend/app/models/device_type.py
@@ -0,0 +1,51 @@
+"""Device type model for network diagrams."""
+import uuid
+from datetime import datetime, timezone
+from typing import Optional, TYPE_CHECKING
+
+from sqlalchemy import String, Boolean, Integer, DateTime, ForeignKey
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.dialects.postgresql import UUID
+
+from app.core.database import Base
+
+if TYPE_CHECKING:
+    pass
+
+
+class DeviceType(Base):
+    """A device type for network diagram nodes (system or team-custom)."""
+    __tablename__ = "device_types"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    slug: Mapped[str] = mapped_column(
+        String(50), nullable=False,
+        comment="Unique identifier used in diagram node data",
+    )
+    label: Mapped[str] = mapped_column(
+        String(100), nullable=False,
+        comment="Display name",
+    )
+    category: Mapped[str] = mapped_column(
+        String(50), nullable=False,
+        comment="network, compute, storage, cloud, endpoint, infrastructure, security",
+    )
+    is_system: Mapped[bool] = mapped_column(
+        Boolean, nullable=False, default=False,
+        comment="True for built-in types that cannot be deleted",
+    )
+    team_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("teams.id", ondelete="CASCADE"),
+        nullable=True,
+        comment="NULL for system types, set for team-custom types",
+    )
+    sort_order: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0,
+        comment="Display order within category",
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )