Castries ( ), population 10,634, aggl. 37,963 (2001-05-12), is the capital city of Saint Lucia, a country in the West Indies. Castries is located at . The district with the same name had a population of 61 341 in 2001-05-22, and stretches over an area of .

Castries is located in a flood plain and is actually built on reclaimed land. It houses the seat of government and the head offices of many of the businesses both foreign and local. The city's design is in a grid pattern similar to a metropolitan city like New York but on a much smaller scale. It has a sheltered harbour which receives cargo vessels and ferry boats as well as cruise ships. It contains duty free shopping facilities such as Point Seraphine and La Place Carinage; many restaurants which offer varied menus from local to Chinese; supermarkets and many other shopping facilities. The city is well serviced by a bus system and taxi service.

St Lucia's main post office is located in Castries. Because most parts of the country do not use standard street addresses, mail is largely sent to P.O. boxes. Any mail sent without a town name ends up in the Castries post office.