A merchant navy or merchant marine is the fleet of merchant vessels that are registered in a specific country. On merchant vessels, seafarers of various ranks and sometimes members of maritime trade unions are required by the International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW) to carry Merchant Mariner's Documents.

King George V bestowed the title of the "Merchant Navy" on the British merchant shipping fleets following their service in the First World War; since then a number of other nations have also adopted use of that title or the similar "Merchant Marine". The following is a partial list of the merchant navies or merchant marines of various countries. In many countries the fleet's proper name is simply the capitalized version of the common noun ("Merchant Navy").