Marines (or naval infantry) are military personnel who primarily operate in littoral zones, both on land and at sea. Historically, the main tasks undertaken by marines have included raiding ashore in support of naval objectives, and the boarding of vessels during combat or capture of prize ships. Marines also help maintain discipline and order aboard the ship (reflecting the pressed nature of the ship's company and the risk of mutiny). In most countries, marines are an integral part of that state's navy; in some countries their marine forces can also instead be part of the land army, such as the French Troupes de Marine, or an autonomous branch such as the United States Marine Corps.
The exact term "marine" is not found in many languages other than English. In French-speaking countries, two terms which could be translated as "marine", but do not translate exactly: troupes de marine (marine troops) and fusiliers-marins (marine riflemen) and fuzileiros navais in Portuguese (lit. 'Naval fusiliers'). The word marine means "navy" in many European languages such as Dutch, French, German, Italian and Norwegian. “Naval infantry” may also refer to sailors forming both temporary and permanent infantry units, such as the British WWI-era 63rd (Royal Naval) Division (an infantry division made-up of Royal Navy sailors on a semi-permanent basis) or the Imperial Japanese Naval Landing Forces (ad-hoc formations of Imperial Japanese Navy sailors temporarily pressed into service as infantry).