Overseas tourists(Non-Chinese passport holders)andTaiwanesemust obtain a Tibet Entry Permit issued by the TTB. Tourists can join a group organized by a travel agency, which will usually handle the permit for them in advance. For individual tourists the offices of the TTB will do it for you....
You can only travel to Tibet in groups organized by a travel agency or by the offices of the Tibet Tourism Bureau. You’d better apply for it at least 15 days ahead of your departure day. Tibet is closed to all foreign visitors in every March according to Tibet government regulations. ...