Hi Stu
In its simplest form; rightclick the Sheet tab, choose View Code, paste this in:
Private Sub Worksheet_Activate()
Call MyMacro
End Sub
Sub MyMacro()
MsgBox "Yo"
End Sub
It runs when you click the sheet's tab. If you need this code to run when activating one
of several windows then you also need to program the Workbook_WindowActivate event in
ThisWorkbook module. Post back if that's relevant and troublesome at the same time.