Udon Thani is one of the best-connected cities in northeast Thailand. By air, the airport (UTH) sits a few kilometres south of the city centre, with frequent and inexpensive flights from Bangkok (around an hour) operated by Thai AirAsia, Thai Lion Air, Nok Air, and Thai Smile. There are also some connections to Phuket and Chiang Mai.
By train, the overnight sleeper from Bangkok's Hua Lamphong (and now Krung Thep Aphiwat) takes around ten hours. It is a comfortable journey if you book a second-class air-conditioned sleeper, and the train pulls into Udon Thani station around dawn. By bus, hourly services from Bangkok's Mo Chit terminal take eight or nine hours.
For travellers continuing north, Udon Thani is also a logical stop on the route to Nong Khai and the Lao border — only an hour by train or songthaew.