Selangor (Jawi script: سلاڠور, population 4.8 million) is one of the 13 states of Malaysia. It is on the west coast of Peninsular Malaysia and is bordered by Perak to the north, Pahang to the east, Negeri Sembilan to the south and the Strait of Malacca to the west. It completely surrounds the federal territories of Kuala Lumpur and Putrajaya.

The origin of the name Selangor is lost in history, although some sources claim the name to have come from the Malay word selangau, 'a large fly' (Musca vicina), most probably due to the abundance of flies in the marshes along the Selangor River in the state's north-west. Another more plausible theory claims the state's name is derived from the term Selang Ur meaning "land of the straits" (ur means "land" in Sanskrit, selang means "straits" in the Malay language).

Selangor is also known by its Arabic honorific, Darul Ehsan ("Abode of Sincerity").

The state is a hereditary constitutional monarchy, of which the reigning Sultan (since 2001) is Sultan Sharafuddin Idris Shah. The Menteri Besar (chief executive of the state government) is currently Tan Sri Abdul Khalid Ibrahim, of the Parti Keadilan Rakyat since 10 March 2008.

The state capital is Shah Alam and the royal capital is Klang. A third major urban centre is Petaling Jaya which was awarded city status on 20 June 2006. Hence, Selangor is one of only two Malaysian states with more than one city; the other being Sarawak.

Selangor is also the richest state in Malaysia in terms of GDP and second richest in terms of GDP per capita (at RM18,157 or US$4,907), behind Penang. On 27 August 2005, Selangor was officially declared the first developed state in Malaysia by the then state government.