Thailand, country located in the centre of mainland Southeast Asia. Located wholly within the tropics, Thailand encompasses diverse ecosystems, including the hilly forested areas of the northern frontier, the fertile rice fields of the central plains, the broad plateau of the northeast, and the rugged coasts along the narrow southern peninsula.

Until the second half of the 20th century, Thailand was primarily an agricultural country, but since the 1960s increasing numbers of people have moved to Bangkok, the capital, and to other cities. Although the greater Bangkok metropolitan area remains the preeminent urban centre in the country, there are other sizable cities, such as Chiang Mai in the north, Nakhon Ratchasima (Khorat), Khon Kaen, and Udon Thani in the northeast, Pattaya in the southeast, and Hat Yai in the far south.