A cruise line is a company that operates cruise ships. Cruise lines have a dual character; they are partly in the transportation business, and partly in the leisure entertainment business, a duality that carries down into the ships themselves, which have both a crew headed by the ship's captain, and a hospitality staff headed by the equivalent of a hotel manager.

Among cruise lines, some are direct descendants of the traditional passenger shipping lines, while others were founded from the 1960s on specifically for cruising. The business is extremely volatile; the ships are massive capital expenditures with ruinous operating costs, and a slight dip in bookings can easily put a company out of business. Cruise lines frequently sell, renovate, or simply rename their ships just to keep up with travel trends.

A wave of failures and consolidation in the 1990s has led to many lines existing only as "brands" within larger corporations, much as a single automobile company produces several makes of cars. Brands exist partly because of repeat customer loyalty, and also to offer different levels of quality and service. For instance, Carnival Corporation owns both Carnival Cruise Lines, whose vessels have a reputation as "party ships" for younger travellers, and Holland America Line, whose ships cultivate an image of classic elegance.

See list of cruise lines.