Cascais (Portuguese pronunciation: [kɐʃˈkajʃ]) is a coastal town in Cascais Municipality in Portugal, 30 kilometres west of Lisbon, with about 35,000 residents. It is a cosmopolitan suburb of the Portuguese capital and one of the richest municipalities in Portugal. The former fishing village gained fame as a resort for Portugal's royal family in the late 19th century and early 20th century. Nowadays, it is a popular vacation spot for both Portuguese and foreign tourists. It is located in the Estoril Coast (named after Estoril, a civil parish), in the Greater Lisbon subregion. It has an airport for general aviation serving the Lisbon Region in Tires (S. Domingos de Rana), Aeroporto Municipal de Cascais.

The coastal settlement of Cascais originated in the 12th century, depending administratively on the town of Sintra, located to the north. In its humble beginnings, Cascais lived from the products of the sea and land, but already in the 13th century, its fish production served the capital Lisbon, located nearby. During the 14th century, the population increased to the outside of the walls of its castle. Its prosperity led to the administrative independence from Sintra in 1364. The village and its surroundings were owned by a feudal lord; the most famous of them was João das Regras (died 1404), a lawyer and professor of the University of Lisbon that was involved in the ascension of King John I to power as the first King of the House of Aviz.