Marines, or naval infantry, are typically a military force trained to operate in littoral zones in support of naval operations. Historically, tasks undertaken by marines have included helping maintain discipline and order aboard the ship (reflecting the pressed nature of the ship's company and the risk of mutiny), the boarding of vessels during combat or capture of prize ships, and providing manpower for raiding ashore in support of the naval objectives. In most countries, the marines are an integral part of that state's navy.

The exact term "marine" does not exist in many languages other than English. In French-speaking countries, two terms exist which could be translated as "marine", but do not translate exactly: troupes de marine and fusiliers-marins; similar pseudo-translations exist elsewhere, e.g. fuzileiros navais in Portuguese (lit. 'Naval fusiliers'). The word marine means "navy" in many European languages such as Dutch, French, German, Italian and Norwegian.