diff --git a/drb-c2-core/app/routers/users.py b/drb-c2-core/app/routers/users.py
index 0cbcbcd..318a259 100644
--- a/drb-c2-core/app/routers/users.py
+++ b/drb-c2-core/app/routers/users.py
@@ -6,6 +6,7 @@ from pydantic import BaseModel
 from firebase_admin import auth as firebase_auth
 from app.internal.auth import require_admin_token
 from app.internal import firestore as fstore
+from app.internal.tenancy import FOUNDING_ORG_ID
 from app.internal import audit
 
 router = APIRouter(prefix="/admin/users", tags=["users"])
@@ -22,9 +23,13 @@ class UserCreate(BaseModel):
     role: str = "viewer"
     display_name: Optional[str] = None
     owned_node_ids: list[str] = []
+    # Org the new user joins as a member. Defaults to the creating admin's own
+    # org — without one, firestore.rules lets the user read nothing at all.
+    org_id: Optional[str] = None
 
 
 class UserUpdate(BaseModel):
+    org_id: Optional[str] = None  # attach an org-less user; defaults to the admin's org
     role: Optional[str] = None
     owned_node_ids: Optional[list[str]] = None
     display_name: Optional[str] = None
@@ -34,6 +39,32 @@ class UserUpdate(BaseModel):
 # Helpers
 # ---------------------------------------------------------------------------
 
+async def _resolve_org(requested: Optional[str], decoded: dict) -> str:
+    """The org a user created/edited here belongs to: the one asked for, else
+    the acting admin's own. Every read the frontend makes is gated on the
+    org_id claim (firestore.rules inOrg()), so a user without one sees no
+    incidents, calls or nodes — which is how admin-created viewers came out
+    before this existed."""
+    # A platform admin needn't have an org claim (isPlatformAdmin reads every
+    # org), so fall back to the founding org every pre-tenancy node, call and
+    # incident was stamped with (app/internal/tenancy.py).
+    org_id = requested or decoded.get("org_id") or FOUNDING_ORG_ID
+    if not await fstore.doc_get("organizations", org_id):
+        raise HTTPException(400, f"Organization '{org_id}' does not exist.")
+    return org_id
+
+
+async def _write_membership(uid: str, email: Optional[str], org_id: str) -> None:
+    """Same org_members shape as POST /auth/signup (routers/links.py)."""
+    await fstore.doc_set("org_members", uid, {
+        "uid": uid,
+        "org_id": org_id,
+        "org_role": "member",
+        "email": email,
+        "added_at": datetime.now(timezone.utc).isoformat(),
+    }, merge=False)
+
+
 def _ms_to_iso(ms: Optional[int]) -> Optional[str]:
     if ms is None:
         return None
@@ -101,6 +132,7 @@ async def create_user(body: UserCreate, decoded: dict = Depends(require_admin_to
         raise HTTPException(400, f"Invalid role. Must be one of: {', '.join(sorted(VALID_ROLES))}")
     if body.role == "operator" and not body.owned_node_ids:
         raise HTTPException(400, "Operator role requires at least one owned node.")
+    org_id = await _resolve_org(body.org_id, decoded)
 
     try:
         fb_user: firebase_auth.UserRecord = await asyncio.to_thread(
@@ -115,10 +147,11 @@ async def create_user(body: UserCreate, decoded: dict = Depends(require_admin_to
         raise HTTPException(400, f"Failed to create user: {e}")
 
     # Set custom claims
-    claims: dict = {"role": body.role, "owned_node_ids": body.owned_node_ids}
+    claims: dict = {"role": body.role, "owned_node_ids": body.owned_node_ids, "org_id": org_id, "org_role": "member"}
     if body.role == "admin":
         claims["admin"] = True
     await asyncio.to_thread(firebase_auth.set_custom_user_claims, fb_user.uid, claims)
+    await _write_membership(fb_user.uid, body.email, org_id)
 
     # Write Firestore profile
     now = datetime.now(timezone.utc).isoformat()
@@ -145,7 +178,7 @@ async def create_user(body: UserCreate, decoded: dict = Depends(require_admin_to
         action="user.create",
         target_uid=fb_user.uid,
         target_email=body.email,
-        details={"role": body.role, "owned_node_ids": body.owned_node_ids},
+        details={"role": body.role, "owned_node_ids": body.owned_node_ids, "org_id": org_id},
     )
 
     return {**_format_user(fb_user), "invite_link": invite_link}
@@ -197,7 +230,20 @@ async def update_user(uid: str, body: UserUpdate, decoded: dict = Depends(requir
     else:
         new_claims.pop("admin", None)
 
+    # Heal users created before POST /users set an org (they could read
+    # nothing): any edit attaches them to the requested/admin's org. An
+    # existing org is never silently moved.
+    attached_org: Optional[str] = None
+    if not existing_claims.get("org_id"):
+        attached_org = await _resolve_org(body.org_id, decoded)
+        new_claims["org_id"] = attached_org
+        new_claims["org_role"] = "member"
+    elif body.org_id and body.org_id != existing_claims["org_id"]:
+        raise HTTPException(400, "User already belongs to another org; moving orgs isn't supported here.")
+
     await asyncio.to_thread(firebase_auth.set_custom_user_claims, uid, new_claims)
+    if attached_org:
+        await _write_membership(uid, fb_user.email, attached_org)
 
     if body.display_name is not None:
         await asyncio.to_thread(firebase_auth.update_user, uid, display_name=body.display_name)
@@ -218,6 +264,7 @@ async def update_user(uid: str, body: UserUpdate, decoded: dict = Depends(requir
             "new_role": new_role,
             "old_nodes": current_nodes,
             "new_nodes": new_nodes,
+            **({"attached_org_id": attached_org} if attached_org else {}),
         },
     )
 
diff --git a/drb-c2-core/tests/test_users_org.py b/drb-c2-core/tests/test_users_org.py
new file mode 100644
index 0000000..7861e85
--- /dev/null
+++ b/drb-c2-core/tests/test_users_org.py
@@ -0,0 +1,85 @@
+"""
+Admin-created users must land in an org. firestore.rules gates every read on
+the org_id claim, so a viewer created via POST /admin/users without one saw no
+incidents or calls at all (reported 2026-09-27).
+"""
+from types import SimpleNamespace
+from unittest.mock import AsyncMock, patch
+
+from fastapi.testclient import TestClient
+
+from app.main import app
+from app.internal.auth import require_admin_token
+from app.routers import users
+
+client = TestClient(app)
+ADMIN = {"uid": "admin-1", "email": "a@x", "role": "admin", "org_id": "org-A"}
+
+
+def _as(decoded):
+    app.dependency_overrides[require_admin_token] = lambda: decoded
+
+
+def teardown_function():
+    app.dependency_overrides.pop(require_admin_token, None)
+
+
+def _fb(**kw):
+    base = dict(uid="u1", email="v@x", display_name="", custom_claims={}, disabled=False,
+                email_verified=False, user_metadata=SimpleNamespace(creation_timestamp=0, last_sign_in_timestamp=None))
+    return SimpleNamespace(**{**base, **kw})
+
+
+def _run(method, path, body, fb_user, orgs=("org-A", "founding")):
+    fa = users.firebase_auth
+    with patch.object(fa, "create_user", return_value=fb_user, create=True), \
+         patch.object(fa, "get_user", return_value=fb_user, create=True), \
+         patch.object(fa, "set_custom_user_claims", create=True) as set_claims, \
+         patch.object(fa, "generate_password_reset_link", return_value="link", create=True), \
+         patch.object(users.fstore, "doc_get", AsyncMock(side_effect=lambda c, i: {"org_id": i} if c == "organizations" and i in orgs else None)), \
+         patch.object(users.fstore, "doc_set", AsyncMock()) as doc_set, \
+         patch.object(users.audit, "write_audit", AsyncMock()):
+        resp = getattr(client, method)(path, json=body)
+    members = [c for c in doc_set.await_args_list if c.args[0] == "org_members"]
+    return resp, set_claims, members
+
+
+def test_created_viewer_joins_the_admins_org_as_member():
+    _as(ADMIN)
+    resp, set_claims, members = _run("post", "/admin/users", {"email": "v@x", "role": "viewer"}, _fb())
+    assert resp.status_code == 200, resp.text
+    claims = set_claims.call_args.args[1]
+    assert (claims["org_id"], claims["org_role"], claims["role"]) == ("org-A", "member", "viewer")
+    assert members and members[0].args[2]["org_id"] == "org-A"
+
+
+def test_admin_without_an_org_claim_defaults_to_founding():
+    _as({k: v for k, v in ADMIN.items() if k != "org_id"})
+    resp, set_claims, _ = _run("post", "/admin/users", {"email": "v@x", "role": "viewer"}, _fb())
+    assert resp.status_code == 200, resp.text
+    assert set_claims.call_args.args[1]["org_id"] == "founding"
+
+
+def test_unknown_org_is_rejected():
+    _as(ADMIN)
+    resp, set_claims, _ = _run("post", "/admin/users", {"email": "v@x", "role": "viewer", "org_id": "nope"}, _fb())
+    assert resp.status_code == 400
+    set_claims.assert_not_called()
+
+
+def test_editing_an_orgless_user_heals_them():
+    _as(ADMIN)
+    resp, set_claims, members = _run("patch", "/admin/users/u1", {"role": "viewer"}, _fb(custom_claims={"role": "viewer"}))
+    assert resp.status_code == 200, resp.text
+    assert set_claims.call_args.args[1]["org_id"] == "org-A"
+    assert members
+
+
+def test_editing_never_silently_moves_an_existing_org():
+    _as(ADMIN)
+    fb = _fb(custom_claims={"role": "viewer", "org_id": "org-B", "org_role": "member"})
+    resp, set_claims, members = _run("patch", "/admin/users/u1", {"role": "viewer"}, fb)
+    assert resp.status_code == 200
+    assert set_claims.call_args.args[1]["org_id"] == "org-B"
+    assert not members
+    assert _run("patch", "/admin/users/u1", {"org_id": "org-A"}, fb)[0].status_code == 400