Not really.

You could embed another workbook into a worksheet (insert|Object|from file).
But that's pretty unusual (in my experience).

Maybe just naming the worksheets would be sufficient:

Main
Main--Sub 01
Main--Sub 02
Main--Sub 03
....



Loni wrote:

Is it possible to have sub-sheets?
I would like to have five main worksheets, and then worksheets under them.

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Dave Peterson