A ship class is a group of ships of a similar design. The navies of the United States and Europe have slightly different traditions where concerns class naming.

In the United States Navy, a class is always named after the lead ship; that is, the first ship of that class to be approved by Congress—almost (but not quite) without exception the ship of the class with the lowest hull number.

In European navies, a class is named after the first ship in commission, regardless of when that ship was ordered or laid down. In some cases, this has resulted in different class names being recorded in European references from their American counterparts - for example, European references report the Colorado class battleships of the United States Navy as "Maryland-class", since USS Maryland (BB-46) was commissioned over two years before USS Colorado (BB-45).

The Royal Navy occasionally gives all ships of a class names that have something in common—perhaps simply all beginning with the same letter—so that class is known not only by the name of its lead ship, but also by whatever their names have in common. Thus, HMS Zulu was a Tribal class destroyer even though there was no ship named HMS Tribal, and the Amphion class of submarines are also known as the "A" class.

Russian (and Soviet) ship classes are formally named by the numbered project that designed them. That project sometimes, but not always, had a metaphorical name, and almost always had a NATO reporting name. In addition, the ships of the class would be numbered, and that number prefixed by a letter indicating the role of that type of vessel. For example, Project 641 had no other name, though NATO referred to its members as Foxtrot class submarines . One boat of that class was B-427—the "B" standing for bolshaya, meaning "large"—which also bore the name Scorpion. In contrast, Project 667AM was known in Russia as Navaga, a type of cod, and was given the NATO reporting name Yankee II. One boat of that class was K-219—the "K" standing for kreyserskaya, "cruiser"—which had no other name. An odd coincidence in ship naming is the Bars-class submarine (NATO reporting name "Akula")—the boats reported in NATO sources as Typhoon class submarines (the fictional Red October was one)—are referred to by the Soviet/Russian forces as Akula class!