You would created a SQL statement (query) based on the values in the combo
boxes and set the Record Source to that SQL statement.

On my website (www.rogersaccesslibrary.com) are a couple of small sample
Access Databases that combined should do what you want.  Look for
"CreateQueries2.mdb" and "ImproveFormPerformance.mdb".  CreateQueries shows
how to create a SQL statement and ImproveFormPerf shows how to set a form's
recordsource to a SQL statement.

Jim:

If values must be selected from all three combo boxes then you only need to
consider the Location and Subprocess values as the Process value  is implied
by the Subprocess value if I understand you correctly.  So the button needs
to build a string expression on which to filter the form:

Lets assume the unbound combo boxes are called cboLocation, cboProcess and
cboSubprocess; don't give them the same names as the fields in the table as
this will cause confusion.  Lets also assume the fields in the table are
Location, ProcessID and SubprocessID.  I'm assuming these are all number data
types.  The code in the button's Click event procedure would go like this:

Conts conMESSAGE = "Both a location and subprocess must be selected."
Dim strFilter As String

' confirm both Location and Subprocess
' values have been selected
If IsNull(Me.cboLocation) Or IsNull(Me.cboSubprocess) Then
   MsgBox conMESSAGE, vbExclamation, "Invalid Operation"
Else
   strFilter = "LocationID = " & me.cboLocation & " And  " & _
       SubprocessID = " & Me.cboSubprocess
  ' filter form
  Me.Filter = strFilter
  Me.FilterOn = True
End If

If on the other and you want each combo box to be optional, i.e. a user can
select form all one, two, three or none then you need to examine each for
Null:

Dim strFilter As String

If Not IsNull(Me.cboLocation) Then
   strFilter = strFilter & _
       " And LocationID = " & Me.cboLocation
End If

If Not IsNull(Me.cboProcess) Then
   strFilter = strFilter & _
       " And ProcessID = " & Me.cboProcess
End If

If Not IsNull(Me.cboSubprocess) Then
   strFilter = strFilter & _
       " And SubprocessID = " & Me.cboSubprocess
End If

' if no values selected then turn form's filter off
' to show all records
If Len(strFilter) = 0
   Me.FilterOn = False
Else
   ' remove redundant leading " And " from filter expression
   strFilter = Mid(strFilter,6)
   ' filter form
  Me.Filter = strFilter
  Me.FilterOn = True
End If

Note that in this case the ProcessID does need to be included in the
criterion as a user may select a process, but not a subprocess.  If they
select both then the former is actually redundant, but it does no harm to
leave it in.

If you want a 'Show All' button on the form as well, then in its Click event
procedure just turn the filter off with:

Me.FilterOn = False

Ken Sheridan
Stafford, England