Conditional summing across multiple worksheets?

Hello,

I am an intermediate Excel user and can't seem to write a function to return the correct information.

I want to conditionally sum information contained on multiple worksheets and then have the sum display on a summary.

I am tallying expenses, each of which is one of four expense type categories. Thus, each worksheet contains columns for description of expense, amount of expense, and expense type. There are numerous worksheets in the workbook, as each worksheet represents a different GL account.

I want to be able to to tell Excel to look through every worksheet in a workbook, find expenses tagged as a specific expense type category, then sum them and display that figure in the summary sheet.

Any help is hugely appreciated!

Thanks,
Mandy