The Review tab
The Proofing group: This group contains potions for revising a Workbook.
Comments group: Comments were located on the Insert menu in Excel 2003.
The Changes group: Replaces the Protection and Share Workbook options on the Tools menu in Excel 2003.
Protect Workbook and Protect Sheet: Prevents other users from permanently changing data within a workbook.
Share Workbook: Allows other users to view and change items in a Workbook.
Track Changes: Allows users to see who has changed a workbook as well as the changes that were made.