Cruisers are mid to large-sized vessels which Starfleet can optimize for a wide variety of general or specialized mission profiles, from exploration, to interdiction, to tactical/defense. Because of this ship type's versatility, Starfleet has created many subcategories for this classification to better designate a given ship's primary function.
Light cruisers fulfill many functions, including diplomatic and courier duties, support for Explorers and larger cruisers in conflict situations, reconnaissance, and patrol of outlying sectors.
Medium cruiser are mid-size, multifunction vessels, able to perform many different duties well. The venerable Miranda class is a representative example. Others include the Steamrunner class, Norway class, and the new Dakota class.
Heavy cruisers often serve as flagships for sector deployment commands or various branches of the fleet. With their heavy armament, they serve at the forefront of many battle taskforces.