The most famous spacecraft design operated by Starfleet, the Constitution class Starships were designed to replace the prehistoric Daedalus class cruisers used in the latter half of the 22nd century. The Constitution class set the standard for future starship designs to come. When launched, the Constitution class represented the ultimate starship design. It was the fastest cruiser, most advanced spaceborne exploration platform and was the most powerful combat starship in the federation.

The 430 officers & crew aboard enjoyed lavish accomidations rivalling those of many luxurious starliners. The same was true of her diplomatic facilities which rivaled those found on larger starbases. The Constitution class was a testbed of sorts, for all kinds of new technology. She was the first class to be equipped with phaser banks, photon torpedos and a relatively new invention, the transporter.By 2272, of the original 12 ships launched, 4 had been lost in the line of duty. The Defiant was lost in an inter-dimensional "interphase", the Constellation was destroyed by an ancient planet killer, the Exeter crew exterminated by some form of bacteriological warfare and the Excalibur was severly damaged during simulated war games with the ill-fated M-5 computer.
Constitution class ships defended the federation against the threats of the day which included multiple incursions by the Klingon and Romulan Empires, dealing with spaceborne entities such as the Amoeba and the planet killer. In 2269, Starfleet Command began a fleet-wide modernization program which revamped the fleet. The remaining Constitution class starships were uprated to Enterprise Class specs. Along with renaming a starship class, Starfleet also adopted Enterprise's Arrowhead emblem throughout the service.