Format([Week Ending],"Short Date") is the creiteria for week ending what is
it for month ending?
What's the context, Frankie? A Format() function translates a field in some
other datatype (date/time perhaps) to a Text string according to a suitable
display format. It's not a criterion, and it will not return a week ending or
a month ending. Your expression simply displays a Date/Time value stored in
the field named [Week Ending] - which could be ANY date, Access won't
interpret the fieldname! - according to the Windows regional date/time Short
Date format.
What's in your table, and what are you trying to accomplish?