Changi (locally /ˈtʃɑːŋi/ CHAHNG-ee) is a planning area located in the geographical region of Tanah Merah in the East Region of Singapore. Sharing borders with Pasir Ris and Tampines to the west, Changi Bay to the southeast, the South China Sea to the east and the Serangoon Harbour to the north. It is further divided into the subzones Changi Airport, Changi Point and Changi West. Changi, excluding the two water catchments and islands of Singapore, is the largest planning area by land size.

Today, Changi is an aviation hub. It is the location of both the Changi Airport and Changi Air Base. Also located within Changi is Singapore's largest prison, Changi Prison. It was used as a Japanese prisoner-of-war camp during the occupation of Singapore in World War II. The prison is Singapore's oldest operating internment facility.

The early Malay place name of Changi was Tanjong Rusa (English: Deer cape), as written in the 1604 Godinho de Eredia map of Singapore.

The name Changi was known in the early 19th century. In the 1828 map by Franklin and Jackson, the extreme southeastern tip of the island is referred to as Tanjong Changi. Vessels using the Johor Straits would have to pass by Changi.

There are many versions of the etymological roots of the name Changi. The first director of the Singapore Botanic Gardens Henry Ridley suggested that it gets its name from a tall tree, Pokok Chengal or Cengal (Malay for Neobalanocarpus heimii, also known as Balanscorpus heimii or Balano scorpas), which was common in the area in the early nineteenth century. It is also written and pronounced as "Chengai". Its heavy timber is commonly used for buildings and furniture and noted for its strength and deep rich colour. Other sources suggests that it comes from a climbing shrub found in the area, the changi ular (Hopea sangal), or chengal asir (Thottea piperiformis).

During the early surveys in the 1820s to 1830s of Singapore island, Changi was also named Franklin Point after Captain Franklin who was involved in these early surveys.

Early Changi was mostly a malaria mosquito infested swampland and jungle that had several kampongs spread across the vast area. Several of these kampongs included from north to south, Kampong Changi, Kampong Telok Paku, Kampong Ayer Gemuroh, Kampong Somapah, Kampong Mata Ikan and Kampong Padang Terbakar, although the exact founding dates of many of these kampongs are unknown. The place was first redeveloped by the British as a summer house and a getaway location from the city centre of Singapore in the 1890s, and was prized for its tranquillity and remoteness. The existence of the resorts there today still bear testament to the original redevelopments there.

Starting from the 1920s due to increasing tension across Asia and Europe in anticipation for war, the British starting building up its military presence at the area and this included the construction of military barracks and the infamous Changi Hospital, with Chinese and Indian labourers brought in from the city. Defences along Changi's southern coast were also beefed up with the construction of machine-gun pillboxes in anticipation of the Imperial Japanese Army arrival by sea. Construction was briefly halted during the Great Depression but was subsequently resumed as these structures were considered vital for the defence of Singapore.