Lhasa Gonggar Airport is the main entry point, 65 kilometres southwest of the city. Direct flights connect Lhasa with Chengdu (the most frequent route, around two hours), Chongqing, Beijing, Shanghai, Xi'an and Kathmandu. Flying in from low altitude is fast but rough on the body — altitude sickness sets in within hours of arrival.
The Qinghai–Tibet Railway is the slower and far better option if you have the time. Trains run daily from Beijing, Xi'an, Shanghai, Chengdu and Xining; the Xining–Lhasa leg is the spectacular section, climbing over the Tanggula Pass at 5,072 metres — the highest railway in the world. Cabins are pressurised and oxygen is piped in. The journey from Xining takes about 21 hours; from Beijing, around 40. Book sleepers well in advance.
All foreigners need a Tibet Travel Permit (TTP) on top of a Chinese visa, plus additional permits for areas outside Lhasa (Everest Base Camp, Mount Kailash, the Nepali border). Permits must be arranged through a licensed Tibetan tour agency — independent travel is not currently allowed. Your agency will need original passport scans roughly three weeks before your arrival date.
Overland from Nepal via the Gyirong border is the other route in, requiring a Group Tourist Visa rather than a regular Chinese visa; it must be coordinated through your tour operator and Nepalese travel agent jointly. The crossing closes for political reasons more often than the airports.