Access/Jet doesn't support triggers (which would make this a trivial
exercise), so instead you must use events ... in the Before or AfterUpdate
Event of your form, you can log the Username and Date/Time (via the Now()
function) to a table, along with any pertinent information you wish to cull
from the record. You could do the same at field level by using the same
function for the Control (for example, a Textbox). You must have either (a)
enable Acces security (in which case you would capture user info via the
CurrentUser method) or (b) have a utility in place to cull the Network User
name to identify the person making the change (get code to retrieve the
Network stuff at mvps.org). It's a lot of work, as you must do this in every
instance where records are updated.