Castries is the capital and largest city of Saint Lucia, an island country in the Caribbean. The urban area has a population of approximately 20,000, while the eponymous district has a population of 70,000, as at May 2013. The city covers 80 km2 (31 sq mi).

Castries is on a flood plain and is built on reclaimed land. It houses the seat of government and the head offices of many foreign and local businesses. The city is laid out in a grid pattern. Its sheltered harbour receives cargo vessels, ferries and cruise ships. It houses duty-free shopping facilities such as Point Seraphine and La Place Carenage.

Castries is the birthplace of Arthur Lewis, winner of the 1979 Nobel Memorial Prize in Economics, as well as of Derek Walcott, winner of the 1992 Nobel Prize for Literature.