I have a user (User A) who has given permissions to another user (User B) to view and modify calendar items. User A now suspects that User B has changed calendar appointments maliciously. How can I go in and look at the modification history for User A's calendar items?

You cannot see modification history. You can see when it was last modified.Bhargav Shukla - MSFT - Exchange Reference: Exchange Server 2007 TechCenter - http://technet.microsoft.com/en-us/library/bb124558.aspx; Exchange Server 2003 TechCenter - http://technet.microsoft.com/en-us/library/bb123872(EXCHG.65).aspx; Microsoft Exchange Team Blog - http://msexchangeteam.com/default.aspx

Yes, double click the meeting in calendar, in the bottom, you could see the last modification time and the editor name. But there isnt a modification history.Thanks,Elvis The Microsoft Exchange Team Blog - You had me at EHLO - http://msexchangeteam.com/