Hanoi or Ha Noi (Vietnamese: Hà Nội / 河內, lit. 'Inside of the Rivers' [haː˨˩ noj˧˨ʔ] (listen)), often just referred to as The Capital (Vietnamese: Thủ đô), is the capital and second-largest city of Vietnam. It covers an area of 3,359.82 km² (1,297.2 sq mi). It consists of 12 urban districts, one district-leveled town and 17 rural districts. It is located within the Red River Delta of Northern Vietnam.

Hanoi can trace its history back to the third century BCE, when a portion of the modern-day city served as the capital of the historic Vietnamese nation of Âu Lạc. Following the collapse of Âu Lạc, the city was part of Han China. In 1010, Vietnamese emperor Lý Thái Tổ established the capital of the imperial Vietnamese nation Đại Việt in modern-day central Hanoi, naming the city Thăng Long (literally 'Ascending Dragon'). Thăng Long remained Đại Việt's political centre until 1802, when the Nguyễn dynasty, the last imperial Vietnamese dynasty, moved the capital to Huế. The city was renamed Hanoi in 1831, and served as the capital of French Indochina from 1902 to 1945. On 6 January 1946, the National Assembly of the Democratic Republic of Vietnam designated Hanoi as the capital of the newly independent country, which would last during the First Indochina War (1946–1954) and the Vietnam War (1955–1975). Hanoi has been the capital of the Socialist Republic of Vietnam since 1976.

A major tourist destination in Vietnam, Hanoi offers well-preserved French colonial architecture, religious sites dedicated to Buddhism, Catholicism, Confucianism and Taoism, several historical landmarks of Vietnamese imperial periods, and a large number of museums. The Central Sector of the Imperial Citadel of Thăng Long in Ba Dinh District was recognized as a UNESCO World Heritage Site in 2010.

Hanoi has a high Human Development Index of 0.799, top amongst all the municipalities and provinces of Vietnam. The city hosts various venerable educational institutions and cultural venues of significance, including the Vietnam National University, the Mỹ Đình National Stadium, and the Vietnam National Museum of Fine Arts. Hanoi was the only Asia-Pacific locality to be granted the "City for Peace" title by the UNESCO on 16 July 1999, recognizing its contributions to the struggle for peace, its efforts to promote equality in the community, protect the environment, promote culture and education, and care for younger generations. Hanoi joined UNESCO's Network of Creative Cities as a Design City on 31 October 2019, on the occasion of World Cities' Day. The city has also hosted numerous political and international events, including APEC Vietnam 2006, 132nd Assembly of the Inter-Parliamentary Union (IPU-132), 2019 North Korea–United States Hanoi Summit, as well as 2009 Asian Indoor Games, and the Southeast Asian Games in 2003 and 2021.