The International 420 Class Dinghy is a double-handed (2 crew) monohull planing dinghy with centreboard, bermuda rig and centre sheeting. The name describes the overall length of the boat in centimeters (the boat is exactly 4.2 meters long). The hull is fibreglass with internal buoyancy tanks. The 420 is equipped with spinnaker and optional trapeze. It has a large sail-area-to-weight ratio, and is designed to plane easily. It can be rigged to be sailed single-handed.

The 420 was designed specifically to be easier to handle than its larger higher-performance cousin, the 470. The 420 was designed by French engineer Christian Maury, as a stepping-stone for club and youth sailing to the 470. The 420 is an International class recognised by the World Sailing.

A derivative of the 420 called the Club 420 is popular in the North America. This class is not recognised by International Sailing Federation or the International 420 Class Association and cannot be used at class events. The boats are very similar in appearance but the Club 420 is slightly stronger and heavier.