diff --git a/amanuensis/backend/membership.py b/amanuensis/backend/membership.py
index 7440353..470964e 100644
--- a/amanuensis/backend/membership.py
+++ b/amanuensis/backend/membership.py
@@ -2,6 +2,10 @@
 Membership query interface
 """
 
+from sqlalchemy.sql.elements import Null
+from sqlalchemy.sql.functions import current_date
+from sqlalchemy.util.langhelpers import NoneType
+from amanuensis.db.models import Lexicon
 from sqlalchemy import select, func
 
 from amanuensis.db import DbContext, Membership
@@ -36,6 +40,27 @@ def create(
     ):
         raise ArgumentError("User is already a member of lexicon")
 
+    # get reference to lexicon for next few checks
+    lex: Lexicon = db(
+        select(Lexicon)
+        .where(Lexicon.id == lexicon_id)
+    ).scalar_one_or_none()
+
+    # Verify lexicon is joinable; current no Lexicons are joinable so this is commented out
+    if not lex.joinable:
+        raise ArgumentError("Can't join: Lexicon is not joinable")
+
+    # Verify lexicon is not full
+    if lex.player_limit:
+        if (
+        db(
+            select(func.count())
+            .where(Membership.lexicon_id == lexicon_id)
+        ).scalar()
+        >= lex.player_limit
+        ):
+            raise ArgumentError("Can't join: Lexicon is full")
+
     new_membership = Membership(
         user_id=user_id,
         lexicon_id=lexicon_id,
diff --git a/tests/conftest.py b/tests/conftest.py
index a93b93c..8e97a6c 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -2,6 +2,7 @@
 pytest test fixtures
 """
 import pytest
+from sqlalchemy.orm import session
 
 from amanuensis.db import DbContext
 import amanuensis.backend.character as charq
@@ -49,7 +50,9 @@ def make_lexicon(db: DbContext):
         }
         state["nonce"] += 1
         updated_kwargs = {**default_kwargs, **kwargs}
-        return lexiq.create(db, **updated_kwargs)
+        lex = lexiq.create(db, **updated_kwargs)
+        lex.joinable = True
+        return lex
 
     return lexicon_factory