ActiveWorkbook Property [Excel 2003 VBA Language Reference]
Returns a Workbook object that represents the workbook in the active window (the window on top). Read-only. Returns Nothing if there are no windows open or if either the Info window or the Clipboard window is the active window.
This example displays the name of the active workbook.
MsgBox "The name of the active workbook is " & ActiveWorkbook.Name
Applies to | Application Object