Not much is known of Réunion's history prior to the arrival of the Portuguese in the early sixteenth century. Arab traders were familiar with it by the name Dina Morgabin. The island is possibly featured on a map from 1153 AD by Al Sharif el-Edrisi. The island might also have been visited by Swahili or Austronesian (Ancient Indonesian-Malaysian) sailors on their journey to the west from the Malay Archipelago to Madagascar.
The first European discovery of the area was made around 1507 by Portuguese explorer Diogo Fernandes Pereira, but the specifics are unclear. The uninhabited island might have been first sighted by the expedition led by Dom Pedro Mascarenhas, who gave his name to the island group around Réunion, the Mascarenes. Réunion itself was dubbed Santa Apolónia after a favourite saint, which suggests that the date of the Portuguese discovery could have been 9 February, her saint day. Diogo Lopes de Sequeira is said to have landed on the islands of Réunion and Rodrigues in 1509.
Over a century later, nominal Portuguese rule had left Santa Apolónia virtually untouched. The island was then occupied by France and administered from Port Louis, Mauritius. Although the first French claims date from 1638, when François Cauche and Salomon Goubert visited in June 1638, the island was officially claimed by Jacques Pronis of France in 1642, when he deported a dozen French mutineers to the island from Madagascar. The convicts were returned to France several years later, and in 1649, the island was named Île Bourbon after the French Royal House of Bourbon. Colonization started in 1665, when the French East India Company sent the first settlers.
"Île de la Réunion" was the name given to the island in 1793 by a decree of the Convention nationale (elected revolutionary constituent assembly) with the fall of the House of Bourbon in France, and the name commemorates the union of revolutionaries from Marseille with the National Guard in Paris, which took place on 10 August 1792. In 1801, the island was renamed "Île Bonaparte", after First Consul Napoleon Bonaparte. The island was invaded by a Royal Navy squadron led by Commodore Josias Rowley in 1810, who used the old name of "Bourbon". When it was restored to France by the Congress of Vienna in 1815, the island retained the name of "Bourbon" until the fall of the restored Bourbons during the French Revolution of 1848, when the island was once again given the name "Île de la Réunion".
From the seventeenth to the nineteenth centuries, French colonisation, supplemented by importing Africans, Chinese and Indians as workers, contributed to ethnic diversity in the population. From 1690, most of the non-Europeans were enslaved. The colony abolished slavery on 20 December 1848. Afterward, many of the foreign workers came as indentured workers. The opening of the Suez Canal in 1869 reduced the importance of the island as a stopover on the East Indies trade route.
During the Second World War, Réunion was under the authority of the Vichy Regime until 30 November 1942, when Free French forces took over the island with the destroyer Léopard.
Réunion became a département d'outre-mer (overseas départment) of France on 19 March 1946. INSEE assigned to Reunion the department code 974, and the region code 04 when regional councils were created in 1982 in France, including in existing overseas departments which also became overseas regions.
Over about two decades in the late twentieth century (1963–1982), 1,630 children from Réunion were relocated to rural areas of metropolitan France, particularly to Creuse, ostensibly for education and work opportunities. That program was led by influential Gaullist politician Michel Debré, who was an MP for Réunion at the time. Many of these children were abused or disadvantaged by the families with whom they were placed. Known as Children of Creuse, they and their fate came to light in 2002 when one of them, Jean-Jacques Martial, filed suit against the French state for kidnapping and deportation of a minor. Other similar lawsuits were filed over the following years, but all were dismissed by French courts and finally by the European Court of Human Rights in 2011.
In 2005 and 2006, Réunion was hit by a crippling epidemic of chikungunya, a disease spread by mosquitoes. According to the BBC News, 255,000 people on Réunion had contracted the disease as of 26 April 2006. The neighbouring islands of Mauritius and Madagascar also suffered epidemics of this disease during the same year. A few cases also appeared in mainland France, carried by people travelling by airline. The French government of Dominique de Villepin sent an emergency aid package worth 36 million Euro (US$57.6M) and deployed approximately five hundred French troops in an effort to eradicate mosquitoes on the island.