Nairobi is the capital and largest city of Kenya. The city lies in the south-central part of Kenya, at an elevation of 1,795 metres (5,889 ft). The name is derived from the Maasai phrase Enkare Nyrobi, which translates to 'place of cool waters', a reference to the Nairobi River which flows through the city. The city proper had a population of 4,397,073 in the 2019 census.

Nairobi is home of the Kenyan Parliament Buildings and hosts thousands of Kenyan businesses and international companies and organisations, including the United Nations Environment Programme (UN Environment) and the United Nations Office at Nairobi (UNON). Nairobi is an established hub for business and culture. The Nairobi Securities Exchange (NSE) is one of the largest stock exchanges in Africa and the second-oldest exchange on the continent. It is Africa's fourth-largest stock exchange in terms of trading volume, capable of making 10 million trades a day. It also contains the Nairobi National Park. Nairobi joined the UNESCO Global Network of Learning Cities in 2010.

Nairobi was founded in 1899 by colonial authorities in British East Africa, as a rail depot on the Uganda - Kenya Railway. It was favoured by the authorities as an ideal resting place due to its high elevation, temperate climate, and adequate water supply. The town quickly grew to replace Mombasa as the capital of Kenya in 1907.

After independence in 1963, Nairobi became the capital of the Republic of Kenya. During Kenya's early period, the city became a centre for the coffee, tea and sisal industries. The successive black governments since independence have built and turned Nairobi into a modern metropolitan city with a diverse population and a growing economy.