Besides a valid Chinese visa, there are another 2 documents required for foreign tourists who want to get to and travel freely in Tibet. One is the entry permit (TTB permit), which you have to obtain it in order to enter Tibet, the other is the Alien's travel permit (PSB permit) if you are planning to travel to some "unopened" areas in Tibet, which you can obtain after you arrive in Tibet.
Also known as Tibet Tourism Bureau (T.T.B.) Permits, is necessary for entry to Lhasa or any other part of Tibet, and is obtained as part of tour arrangements for travel to Tibet.
When you fly from any city to Lhasa, you will need to show this permit upon checking in at the airport. Furthermore, whenever you buy a flight to Lhasa you need to show this permit. TTB permits are also needed in groups traveling by Land Cruiser, but this will be arranged by the travel agency.
How to apply for it?
You can ONLY apply through a TTB authorized travel agency (most in Tibet or Chengdu) by providing the necessary info. to them. After receiving your data, they will work with the T.T.B to process it for you. Suggest you apply for the permit at least 10 days prior to your entry date.
1) If you do not book any service(such as air tickets, land cruiser with driver, guide or tour package ) from the travel agency, they will refuse to get you the permits, as no travel agency provides "permit-only" service.
2) The process is not applicable for diplomats, journalists and government officials, who can only travel to Tibet under the arrangement of the Foreign Affairs Office of Tibet Government.
How to obtain it?
There are two ways leading to Tibet, one is from other parts of China, the other is from Nepal.
If you enter Tibet from other places of China, you can claim for it from your travel agency's local office in that city, e.g. Chengdu if by air, Golmud if by Qinghai-Tibet Highway. It is a must document when you are boarding the air to Tibet.
If you enter Tibet from Nepal, you can obtain the fax copy of this permit from the Chinese Embassy in Katmandu. After you land at Lhasa, their guide will meet you (at the Lhasa airport or at the Border if you travel though friendship highway) and forward the original Permit to you.
If you want to go further to some "unopened" areas in Tibet, you need an Alien's travel permit issued by PSB of Tibet. It is called "Alien's Travel Permit" or "PSB permit", issued by the Foreign Affairs Section of the Local Public Security Bureau (PSB).
How to apply for it?
You also need to get through a travel agency. There is a statement that "Lhasa PSB will not issue travel permits to individuals but will direct you to a travel agency. Agencies can arrange a travel permit to almost anywhere but only if you book a Land Cruiser, driver and a guide". Though it doesn't make much sense, but nothing we can do to change the situation. It normally takes a few hours and the cost is around Y50/person.
Which parts of Tibet are listed as "unopened" areas?
Tsetang: Samye Monastery, Tomb of Tibetan King, Changdruk Temple, Yumbulakhang
Shigatse: Sakya Monastery, The MT Everest, Rongbuk Monastery
Gyangtse: Pelkor Chode Monastery & Kubum Stupa
Nqari Region; Basumtso lake in Nyingchi Region;
Tips for applying for a China visa
You'd better NOT mention Tibet as your destination when applying for a visa to China. After getting your China visa, you can easily get a Tibet permit. Otherwise you have to wait for Tibet permit and then you can get China visa.