diff --git a/app/main.py b/app/main.py
index ee9122f..f9c4f98 100644
--- a/app/main.py
+++ b/app/main.py
@@ -175,6 +175,16 @@ LOOMIO_API_KEY = os.environ.get("LOOMIO_API_KEY", "")
 # mangled auto-handle (email local-part + random suffix). The B3 users API
 # lets us rename them to the member's Cloudron username.
 LOOMIO_B3_KEY = os.environ.get("LOOMIO_B3_KEY", "")
+
+# Matrix homeserver (self-hosted Synapse at matrix.inference.coop). The bot
+# account (admin) invites every active member to the co-op Space on sync.
+# Members authenticate via Cloudron SSO; their homeserver MXID is
+# @<cloudron-username>:inference.coop. Federated MXIDs (external servers)
+# can also be invited directly.
+MATRIX_HOMESERVER = os.environ.get("MATRIX_HOMESERVER", "https://matrix.inference.coop")
+MATRIX_BOT_TOKEN = os.environ.get("MATRIX_BOT_TOKEN", "")
+MATRIX_SPACE_ID = os.environ.get("MATRIX_SPACE_ID", "")
+MATRIX_GENERAL_ROOM = os.environ.get("MATRIX_GENERAL_ROOM", "")
 LOOMIO_GROUP_ID = os.environ.get("LOOMIO_GROUP_ID", "")
 # Operator accounts that must always remain in the Loomio group (never removed
 # by the remove_absent reconciliation), comma-separated.
@@ -823,6 +833,80 @@ async def loomio_fix_usernames(client: httpx.AsyncClient) -> dict:
     return {"fixed": fixed, "skipped": skipped}
 
 
+async def sync_matrix_space() -> dict:
+    """Invite every active member to the co-op Matrix Space (and General room).
+
+    Members log in via Cloudron SSO, so their local MXID is
+    @<username>:inference.coop. We resolve the Cloudron username for each
+    active member email and invite them if not already in the space.
+    Best-effort: missing config just skips; failures log and continue.
+    """
+    if not (MATRIX_BOT_TOKEN and MATRIX_SPACE_ID):
+        logger.info("Matrix space sync skipped (not configured)")
+        return {"skipped": True}
+    H = {"Authorization": f"Bearer {MATRIX_BOT_TOKEN}", "Content-Type": "application/json"}
+
+    async def invite(mxid: str, room: str) -> None:
+        r = await client.post(
+            f"{MATRIX_HOMESERVER}/_matrix/client/v3/rooms/{room}/invite",
+            headers=H, json={"user_id": mxid},
+        )
+        # 200 = invited; 403 M_FORBIDDEN with 'already in room' is fine too
+        if r.status_code not in (200, 403) and "already" not in r.text:
+            logger.warning("Matrix invite %s -> %s failed: %s %s",
+                           mxid, room, r.status_code, r.text[:120])
+
+    async with httpx.AsyncClient(timeout=30) as client:
+        # current members of the space (to avoid duplicate invites)
+        r = await client.get(
+            f"{MATRIX_HOMESERVER}/_matrix/client/v3/rooms/{MATRIX_SPACE_ID}/joined_members",
+            headers=H)
+        joined = set(r.json().get("joined", {}).keys()) if r.status_code == 200 else set()
+        # also pending invites
+        r = await client.get(
+            f"{MATRIX_HOMESERVER}/_matrix/client/v3/rooms/{MATRIX_SPACE_ID}/members?membership=invite",
+            headers=H)
+        invited = {m["state_key"] for m in r.json().get("chunk", [])} if r.status_code == 200 else set()
+
+        invited_count = 0
+        async for email, mxid in matrix_member_mxids(client):
+            if not mxid or mxid in joined or mxid in invited:
+                continue
+            await invite(mxid, MATRIX_SPACE_ID)
+            if MATRIX_GENERAL_ROOM:
+                await invite(mxid, MATRIX_GENERAL_ROOM)
+            invited_count += 1
+        if invited_count:
+            logger.info("Matrix space invites sent: %s", invited_count)
+    return {"invited": invited_count}
+
+
+async def matrix_member_mxids(client: httpx.AsyncClient):
+    """Yield (email, mxid) for each active member.
+
+    Local members log in via Cloudron SSO and Synapse names them by Cloudron
+    username → @<username>:inference.coop. Emails that don't resolve to a
+    Cloudron user (e.g. federated/external members) are skipped here but can
+    be added via the MATRIX_EXTRA_MXIDS env (comma list of full MXIDs).
+    """
+    extra = [m.strip() for m in os.environ.get("MATRIX_EXTRA_MXIDS", "").split(",") if m.strip()]
+    seen: set[str] = set()
+    r = await client.get(
+        f"{CLOUDRON_API}/api/v1/users",
+        headers=cloudron_headers(),
+    )
+    users = {u["email"].lower(): u["username"] for u in r.json()} if r.status_code == 200 else {}
+    for email in await get_active_member_emails():
+        username = users.get(email.lower())
+        if username:
+            mxid = f"@{username}:inference.coop"
+            seen.add(mxid)
+            yield email, mxid
+    for mxid in extra:
+        if mxid not in seen:
+            yield mxid, mxid
+
+
 async def sync_loomio_memberships() -> None:
     """Reconcile the Loomio group to the current active-member list.
 
@@ -1139,6 +1223,7 @@ async def provision_member(email: str, name: str, slug: str = "") -> str:
         logger.warning("Held-credit grant for %s failed: %s", email, e)
 
     await sync_loomio_memberships()
+    await sync_matrix_space()
     logger.info("Provisioned member %s (user_id=%s)", email, user_id)
     return user_id
 
@@ -1581,6 +1666,7 @@ async def opencollective_webhook(request: Request, token: str):
                 deactivate_member(member["email"])
                 await listmonk_sync(member["email"], subscribe=False)
                 await sync_loomio_memberships()
+                await sync_matrix_space()
                 logger.info("Deactivated member %s (slug=%s)", member["email"], slug)
                 return JSONResponse({"status": "deactivated", "email": member["email"]})
         return JSONResponse({"status": "deactivated", "note": "no matching member"})
@@ -1739,6 +1825,7 @@ async def admin_sync_loomio(request: Request):
     _verify_admin_token(request)
 
     await sync_loomio_memberships()
+    await sync_matrix_space()
     return {"status": "synced"}
 
 
@@ -2456,6 +2543,7 @@ async def reconcile_memberships() -> dict:
 
     # 3. Sync Loomio.
     await sync_loomio_memberships()
+    await sync_matrix_space()
 
     return {
         "status": "reconciled",