Some cruise lines have specialties; for example, Saga Cruises only allows passengers over 50 years old aboard their ships, and Star Clippers and formerly Windjammer Barefoot Cruises and Windstar Cruises only operate tall ships. Regent Seven Seas Cruises operates medium-sized vessels—smaller than the "megaships" of Carnival and Royal Caribbean—designed such that 90% of their suites are balconies. Several specialty lines offer "expedition cruising" or only operate small ships, visiting certain destinations such as the Arctic and Antarctica, or the Galápagos Islands.
Currently the five largest cruise line operators in the world are Carnival Corporation & plc, Royal Caribbean Cruises Ltd., Star Cruises (which owns 50% of Norwegian Cruise Line; NCL in its own right is the third largest line), MSC Cruises, and Louis Cruise Lines. Louis Cruises has largely grown its fleet through purchasing older second- or third-hand ships, while the other four operators have largely constructed their own vessels and combined own the majority of the "megaships".