Castries (/kəˈstriːz/ ⓘ) is the capital and largest city of Saint Lucia, an island country in the Caribbean.

[7] It adopted the name Castries in 1756, in honor of Charles Eugène Gabriel de La Croix, marquis de Castries, whose title relates to a commune in southern France; the origin for the commune's name is the Latin word castra, plural of castrum ("fortified field", or "strong castle, fortified city" by extension).

[7] In 1835, the British built the western wharf in 1642 to facilitate the coal trade and the first steamship arrived in 1841, the RMS Solway.

[7]: 163, 243–244 During World War II on 9 March 1942, the German U-161 sailed into Castries harbor at night and sank two allied ships,[7]: 275 [9] including the Canadian ocean liner RMS Lady Nelson, which was subsequently refloated in the harbour and taken to Canada to be converted to a hospital ship.

[11] Landmarks include the Cathedral of the Immaculate Conception, Derek Walcott Square (renamed from Columbus Square to honour the island's Nobel Prize-winning poet, Derek Walcott), the City Library, the Government House, Castries Market, and Fort Charlotte, at the top of Morne Fortune (an 845-foot or 258 m hill).

The buses are private (not subsidized by government) bearing green license plates with numbers that start with an M—for example, M456.

As well as being the capital city of Saint Lucia, Castries hosts the secretariat of the Organisation of Eastern Caribbean States.