Please look the map above. One thing here need to clarify is that where is known as "Tibet" by most of travelers is actually "Tibet Autonomous Region" and you are required to obtain a permit to enter. And apart from it, you can also find some "Tibetan Autonomous Prefectures" which are partly located in following four provinces: Qinghai Province, Southwest Gansu Province, West and North Sichuan and North Yunnan Province where you actually don't need to travel with permit except very few places that you need to get a certain permit from police.

There are three kinds of permit you need to understand:

1. Tibet Travel Permit
Since "Tibet" is one part of China, you won't need to obtain any other Visa for it once you arrived in China. As it is an area not fully opened to tourists, you must obtain a "Tibet Travel Permit" before your departure to "Tibet Autonomous Region". Here are three major cities to get into "Tibet Autonomous Region": Beijing, Chengdu and Xining, though expensive Landcruiser trip from Yunnan to Lhasa is also possible and you can also find plane ticket to Lhasa from remote Zhongdian(Shangri-la). If you are going to take train from the cities listed above, you must get the original copy of Permit while you might not see Permit at all if you choose to fly but the Permit is in fact stored in Travel agency which hostel or guesthouse uses. And also you should be wared that this "Tibet Travel Permit" is only effective in "Lhasa Municipality" which covers Lhasa City, Nam Tso, Nagchu, Amdo town, Ganden monastery, Shigatse and a few other smaller places. Should you venture to other places outside Lhasa Municipality, you need to get another permit which is called "Alien Travel Permit".

(There is a rumor that the "Tibet Travel Permit" would be gone after train to Lhasa started, but so far the policy still not changed. Some may get suggested by other travelers that they were not checked when they travel to Tibet, but that just because they are lucky. If you get caught without "Tibet Travel Permit", you can be taken to Police Station , fined and sent back to where you started your trip before.)

2. Alien Travel Permit
"Alien Travel Permit" is easy and quick to get in Lhasa or Shigatze. If you follow an expensive 4WD trip, this permit is included, you won't need to pay. But if you would like to travel by your own down the Friendship Highway to border town Zhangmu of Nepal and visit some interesting places such like Sakya Monastery and Everest Base Camp, you should get "Alien Travel Permit" before you go. Price of this Permit costs you approximately 100 Yuan, same price in Shigatze. There are some checkpoints on the way to Zhangmu, You can be fined if you are caught without it.

3. Military Permit
To travel to the southern and western bounderies of Tibet, apart from "Tibet Travel Permit" and "Alien Travel Permit", another "Military Permit" is also a must. Most of people going there to visit Mt. Kailash, Guge Kingdom or do the overland trip through Xinzang Road (the road lies between Xinjiang Urgur Autonomous Region and Tibet Autonomous Region) to Kashgar or travel in Nyingtri Prefecture. Since you are not allowed to travel by your own, the "Military Permit" can be only arranged by Travel agency and you have to go by 4WD.

4. Enter Tibet from Nepal or from Lhasa to Nepal
Enter Tibet from Nepal that you have to go with a group which can be arranged by local travel agency in Tamel, Kathmandu. Don't try to obtain a Chinese Visa if you intead to enter Tibet from Nepal side, it will just waste your money, because enter to Tibet from Nepal side a regualr Chinese Visa is not effective. You should leave all the jobs to your travel agency and then enjoy your trip. Definitely it's more expensive than travel from Tibet to Nepal, which is better because at least you can travel by your own down the Friendship Highway. The time I (mix) was in Lhasa, the international bus from Lhasa to border town Zhangmu was pended due to some reasons(end of 2006), but there were always some long distance bus drivers waiting in front of Nepalese Consulat to collect passengers to border town Zhangmu. They didn't receive foreigners in Lhasa. But the bus will stop in Shigatze for lunch and receive foreign travelers in the bus station and then bring them all the way to Zhangmu. Some checkpoints are on the way, our bus stoped several times just for soldier checking passengers' passport and permit. The bus took 18 hours to Zhangmu, and you can expect better exchange rate in this border town than in Kathmandu. From Zhangmu to border custom you need to walk for a while and can expect waiting in a long line. After custom there is also a long way to walk, so i suggest you to share a bus with other travelers. The bus driver will take you to custom, then picks you at another side of custom and then drives you to Nepalese Custom. After passing Nepalese Custom, you'll encounter many touts, bus drivers and private jeep drivers, usually it costs 400-500 Rs/Per person to Kathmandu by sharing a Jeep with other travelers.

5. Enter to Tibet from Qinghai
From Qinghai to Tibet you can either take the train from Xining or catch a bus from Golmud. You are required to have "Tibet Travel Permit".

6. Enter to Tibet from Sichuan
It is difficult to do the overland trip by your own from Chengdu to Lhasa though this route is considered as the best, however it's possible to go with expensive 4WD tour.(travel agency helps you to arrange all the necessary permits that you need to have). Most of people get good deal and fly to Lhasa from Chengdu while some choose to take the train. You are required to have "Tibet Travel Permit".

7. Enter to Tibet from Yunnan
You can fly from Zhongdian (Shangri-la) to Lhasa with a "Tibet Travel Permit", or try the expensive 4WD tour.

8. Enter to Tibet From Kashgar, Xinjiang Urgur Autonomous Region
This route is forbidden to travel by your own, the only way is to join a 4WD tour.(travel agency helps you to arrange all the necessary permits that you need to have).

8. Enter to Tibet From India/Sikkim and Bhutan
So far, no way!

Just keep this in mind: Travel to Tibet or those restricted area in T.A.R without proper permit mentioned above, you can expect be fined, detained in police station or sent back to where you started your trip. If you made your trip without permit and problem, that doesn't mean that you are not required a permit, only because you are a lucky guy. Good luck and enjoy your trip.