Hi mjj,
If you want to Tibet travel, You must have Tibet Entry Permit. The Tibet permit is Tibet Tourism Bureau (TTB) Permit.Tibet Tourism Bureau (TTB) Permits are necessary for entry to Lhasa or any other part of the Tibetan Autonomous Region, and are obtained through tour operators as part of arrangements for travel; A T.T.B. permit does not obviate the need for an Aliens’ Travel Permit for any closed areas that may be visited.
But you can get them easily from your travel agent like www.traveltibetguide.com.

According to the government rule, Tibet Entry Permit is required before the international tourists entering the area. When you take flights from other cities into Tibet, you might be asked to show your permit at security check. If taking train, it seems that no one is handling the check. But after your arrival in Tibet, if you don't have the permit and get caught, there might be some problems. To get a Tibet entry permit, you need to book a tour (even a simple package) with a Chinese tour company, which can help you to apply for the permit. For more info, you can visit http://www.tibettraintravel.com/TravelDocument.htm.

Good luck!

Once you book tour in Tibet, your travel agency can be your representative to apply for the permit for you. But please confirm your tour at least two weeks prior to your arrival so that the agency has enough time for the application. To apply for the permit, the copies of passport and visa are required.

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