Bangkok traces its roots to a small trading post during the Ayutthaya Kingdom in the 15th century, which eventually grew in size and became the site of two capital cities: Thonburi in 1768 and Rattanakosin in 1782. Bangkok was at the heart of Siam's (as Thailand used to be known) modernization, during the later 19th century, as the country faced pressures from the West. The city was the centre of Thailand's political struggles, throughout the 20th century, as the country abolished absolute monarchy, adopted constitutional rule and underwent numerous coups and several uprisings. The city grew rapidly during the 1960s through the 1980s and now exerts a significant impact among Thailand's politics, economy, education, media and modern society.

The Asian investment boom in the 1980s and 1990s led many multinational corporations to locate their regional headquarters in Bangkok. The city is now a major regional force in finance and business. It is an international hub for transport and health care, and has emerged as a regional centre for the arts, fashion and entertainment. The city is well known for its vibrant street life and cultural landmarks, as well as its notorious red-light districts. The historic Grand Palace and Buddhist temples including Wat Arunand Wat Pho stand in contrast with other tourist attractions such as the nightlife scenes of Khaosan Road and Patpong. Bangkok is among the world's top tourist destinations. It is named the most visited city in MasterCard's Global Destination Cities Index, and was named "World's Best City" for four consecutive years by Travel + Leisure magazine.

Bangkok's rapid growth amidst little urban planning and regulation has resulted in a haphazard cityscape and inadequate infrastructure systems. Limited roads, despite an extensive expressway network, together with substantial private car usage, have resulted in chronic and crippling traffic congestion. This in turn caused severe air pollution in the 1990s. The city has since turned to public transport in an attempt to solve this major problem. Four rapid transit lines are now in operation, with more systems under construction or planned by the national government and the Bangkok Metropolitan Administration.

Bangkok's economy gradually expanded through busy international trade, first with China, then with Western merchants returning in the early-to-mid 19th century. As the capital, Bangkok was the centre of Siam's modernization as it faced pressure from Western powers in the late 19th century. The reigns of Kings Mongkut (Rama IV, 1851–68) and Chulalongkorn (Rama V, 1868–1910) saw the introduction of the steam engine, printing press, rail transport and utilities infrastructure in the city, as well as formal education and healthcare. Bangkok became the centre stage for power struggles between the military and political elite as the country abolished absolute monarchy in 1932. It was subject to Japanese occupation and Allied bombing during World War II, but rapidly grew in the post-war period as a result of United States developmental aid and government-sponsored investment. Bangkok's role as an American military R&R destination boosted its tourism industry as well as firmly establishing it as a sex tourism destination. Disproportionate urban development led to increasing income inequalities and unprecedented migration from rural areas into Bangkok; its population surged from 1.8 to 3 million in the 1960s. Following the United States' withdrawal from Vietnam in 1973, Japanese businesses took over as leaders in investment, and the expansion of export-oriented manufacturing led to growth of the financial market in Bangkok.Rapid growth of the city continued through the 1980s and early 1990s, until it was stalled by the 1997 Asian financial crisis. By then, many public and social issues had emerged, among them the strain on infrastructure reflected in the city's notorious traffic jams. Bangkok's role as the nation's political stage continues to be seen in strings of popular protests, from the student uprisings in 1973 and 1976, anti-military demonstrations in 1992, and successive anti-government demonstrations by the "Yellow Shirt", "Red Shirt" and "Light blue Shirt" movements from 2008 onwards.

Administration of the city was first formalized by King Chulalongkorn in 1906, with the establishment of Monthon Krung Thep Phra Maha Nakhon (มณฑลกรุงเทพพระมหานคร) as a national subdivision. In 1915 the monthon was split into several provinces, the administrative boundaries of which have since further changed. The city in its current form was created in 1972 with the formation of the Bangkok Metropolitan Administration (BMA), following the merger of Phra Nakhon Province on the eastern bank of the Chao Phraya and Thonburi Province on the west during the previous year.[8