This list organizes the largest cruise ships by their respective classes in the cruise lines. Each cruise line define their own collection of cruise ship classes, using classes to differentiate cruise ships based on their physical characteristics, range of services provided and quality of comfort.

Royal Caribbean International, one of the largest cruise lines, has at least eight classes of cruise ships, from the Voyager-class vessels that entered services since 1999 to the more recent Quantum- and Oasis-class gigantic cruise ships.

Another large cruise line, MSC Cruises, has launched at least 3 new classes in the past 10 years, from the Fantasia-class cruises to the Seaside-class ships to the larger Meraviglia-class cruise ships, the largest of which is the MSC Grandiosa or "Greatness at Sea" (as of March 2020).