Kuala Lumpur, officially the Federal Territory of Kuala Lumpur, and colloquially referred to as KL, is the capital city and a federal territory of Malaysia. It is the largest city in the country, covering an area of 243 km2 (94 sq mi) with a census population of 2,075,600 as of 2024. Greater Kuala Lumpur, also known as the Klang Valley, is an urban agglomeration of 8.8 million people as of 2024. It is among the fastest growing metropolitan regions in Southeast Asia, both in population and economic development.

The city serves as the cultural, financial, tourism, political and economic centre of Malaysia. It is also home to the bicameral Parliament of Malaysia (consisting of the Dewan Rakyat and the Dewan Negara) and the Istana Negara, the official residence of the Yang di-Pertuan Agong (monarch of Malaysia). Kuala Lumpur was first developed around 1857 as a town serving the tin mines of the region, and important figures such as Yap Ah Loy and Frank Swettenham were instrumental in the early development of the city during the late 19th century. It served as the capital of Selangor from 1880 until 1978. Kuala Lumpur was the founding capital of the Federation of Malaya and its successor, Malaysia. The city remained the seat of the executive and judicial branches of the Malaysian federal government until these were relocated to Putrajaya in early 1999. However, some sections of the political bodies still remain in Kuala Lumpur. The city is one of the three Federal Territories of Malaysia, enclaved within the state of Selangor, on the central west coast of Peninsular Malaysia.

Since the 1990s, the city has played host to many international sporting, political and cultural events, including the 1998 Commonwealth Games, 2001 Southeast Asian Games, 2017 Southeast Asian Games, Formula One, Moto GP and FIFA World Youth Championships. Kuala Lumpur has undergone rapid development in recent decades and is home to the tallest twin buildings in the world, the Petronas Towers which have since become an iconic symbol of Malaysian development. Kuala Lumpur is well connected with neighboring urban metro regions such as Petaling Jaya via the rapidly expanding Klang Valley Integrated Transit System. Residents of the city can also travel to other parts of Peninsular Malaysia as well as to Kuala Lumpur International Airport (KLIA) via rail through KL Sentral.

Kuala Lumpur was ranked the 6th most-visited city in the world on the Mastercard Destination Cities Index in 2019. The city houses three of the world's ten largest shopping malls. Kuala Lumpur ranks 70th in the world and the second in Southeast Asia after Singapore for the Economist Intelligence Unit's Global Liveability Ranking and ninth in ASPAC and second in Southeast Asia after Singapore for KPMG's Leading Technology Innovation Hub 2021. Kuala Lumpur was named World Book Capital 2020 by UNESCO. In 2024, Kuala Lumpur was ranked second for the best outstanding city in Southeast Asia, after Singapore, and 135th in the world by the Oxford Economic Papers' Global Cities Index.