Yep, UNION queries are great for what they do, but Access has issues with updates of any kind, probably because of difficulties in finding the targeted record for the writeback. When you generated the UNION query, you REALLY generated a single list of records taken from all contributing SELECT queries. But that list (to the best of my understanding) is actually just a list of record file addresses (i.e. where ON THE DISK to find the records). It does not (again, to the best of my understanding) include the source table for each record, so the update function (and, for that matter, DELETE) will not know which table to update. And the append query has the same issue - more than one possible table. It is the ambiguity of location that makes the problem difficult.