What permit required before traveling to Tibet?

Tibet Travel Permit is the official document which permits the foreign traveler to enter and travel in Tibet. It is the secondary travel document to travel in Tibet besides the China Visa. Among several Tibet permits, Tibet Travel Permit (Tibet Entry Permit) is foremost and compulsory for foreign passport holders to enter Tibet. The Permit is issued by Tibet Tourism Bureau and it is the so-called Tibet Tourism Bureau Permit or TTB Permit. With this permit, foreigners can visit Lhasa, Shigatse, Everest, Mt Kailash, and so on. Tibet Travel Permit is also needed to take a train or flight to and off Tibet. You must contact the Tibetan Travel Agency based in Lhasa to process the Tibet Travel Permit before starting your Tibet tour.