Some of the differences are subtle, but today's cruise lines largely fall into three basic categories: mainstream, premium, and luxury. There are also a couple of secondary categories to consider, including river/barge and specialty cruise lines.

The cruise industry generally categorizes vessels into three primary types: Ocean Cruises, River Cruises, and Expedition Cruises. Ocean Cruises are the most common, featuring large "floating resorts" that carry thousands of passengers and offer extensive amenities like Broadway-style shows, water parks, and multiple dining venues. They primarily sail the Caribbean, Mediterranean, and Alaska. River Cruises utilize much smaller, long and narrow ships designed to navigate inland waterways like the Rhine, Danube, or Mekong. These focus on "destination immersion," docking in the heart of cities and offering a more intimate, all-inclusive experience. Expedition Cruises use rugged, ice-strengthened vessels designed for remote and "off-the-beaten-path" destinations like Antarctica, the Galápagos, or the Arctic. These ships emphasize education and adventure, often featuring a team of naturalists and a fleet of Zodiacs for landings, providing a stark contrast to the entertainment-heavy focus of mainstream ocean liners.