Abuja () is the capital and sixth most populous city of Nigeria. Situated in the middle of the country within the Federal Capital Territory (FCT), it is a planned city built mainly in the 1980s based on a master plan by International Planning Associates (IPA), a consortium of three American planning and architecture firms made up of Wallace, Roberts, McHarg & Todd (WRMT – a group of architects) as the lead, Archi systems International (a subsidiary of the Howard Hughes Corporation), and Planning Research Corporation. The Central Business District of Abuja was designed by Japanese architect Kenzo Tange. It replaced Lagos, the country's most populous city, as the capital on 12 December 1991.

Abuja's geography is defined by Aso Rock, a 400-metre (1,300 ft) monolith left by water erosion. The Presidential Complex, National Assembly, Supreme Court and much of the city extends to the south of the rock. Zuma Rock, a 792-metre (2,598 ft) monolith, lies just north of the city on the expressway to Kaduna.

At the 2006 census, the city of Abuja had a population of 776,298 and 179,674 households making it one of the ten most populous cities in Nigeria (placing eighth as of 2006). According to the United Nations, Abuja grew by 139.7% between 2000 and 2010, making it the fastest-growing city in the world. As of 2015, the city is experiencing an annual growth of at least 35%, retaining its position as the fastest-growing city on the African continent and one of the fastest-growing in the world. As of 2016, the metropolitan area of Abuja is estimated at six million people, placing it behind only Lagos as the most populous metro area in Nigeria.

Major religious sites include the Nigerian National Mosque and the Nigerian National Christian Centre. The city is served by the Nnamdi Azikiwe International Airport. Abuja is known for being one of the few purpose-built capital cities in Africa, as well as being one of the wealthiest.

Abuja is Nigeria's administrative and political capital. It is also a key capital on the African continent due to Nigeria's geo-political influence in regional affairs. Abuja is also a conference centre and hosts various meetings annually, such as the 2003 Commonwealth Heads of Government meeting and the 2014 World Economic Forum (Africa) meetings. Abuja joined the UNESCO Global Network of Learning Cities in 2016.