Hi, Is the Calendar tab showing in the Mail Toolbar at the top of the window ? If not, then it could be something to do with the 'Lightning' extension which is need in order to get the calendar to work. It happened to me some while back ... one minute the Calendar was there, then the next it was gone after an update to the main Thunderbird program. The solution was to update the Lightning extension as the old one was not compatible with the newer version of the program. I believe that the latest version of Lightning is v3.3.2 ... you should check from the Tools option in the Menu Bar Hope this helps