There is no way to do this when entering data directly into tables, unless
using a server database engine such as SQL Server that supports triggers. If
you're not using a server database engine that supports triggers, you will
need to ensure that data is always entered via forms, and add code to the
AfterInsert (if you just need to record records once, when they are first
added) or AfterUpdate (if you also need to record modifications to
previously entered records) event procedure of the form to add the data to
the other table. Here's an example that copies only new records ...
Private Sub Form_AfterUpdate()
CurrentProject.Connection.Execute _
"INSERT INTO Table2 (TwoText) VALUES ('" & _
Me!OneText & "')"
End Sub
.... where 'Table2' is the name of the second table, 'TwoText' is the name
of the field in the second table, and 'OneText' is the name of the control
on the form.