The International 420 Dinghy is a sailing dinghy popular for racing and teaching. The hull is fiberglass with internal buoyancy tanks. The 420 has a bermuda rig, spinnaker and trapeze. It has a large sail-area-to-weight ratio, and is designed to plane easily. The 420 is an International class recognised by World Sailing. The name refers to the boat's length of 420 centimetres (4.2 m; 13 ft 9 in).

The International 420 was designed by Christian Maury in France in the year 1959. The class developed rapidly in France, being adopted nationally as a youth trainer for the larger Olympic class International 470. By the late 1960s the class was adopted by a few UK university sailing clubs for training and team racing.

The Club 420, or C420,^[5] is a derivative of the 420 and is not recognized by World Sailing or the International 420 Class Association. Designed by Vanguard boats in the 1970s, it has a heavier hull, reinforced for durability in institutional sailing, and a stiff, untapered mast. The boat is much more simple to sail, yet lacks the performance of the original dinghy due to its extra weight. The Club 420 is used extensively on the youth race circuit in the US, with over 5,000 boats in North America,^[6] but is not sailed in most other countries. It cannot be used at I420 class events.

The Z420 is a transformation of the Club 420. The Z420 hull is 50 pounds (23 kg) lighter and 40 percent stiffer than the C420. Whereas a C420 hull is composed of six pieces, the Z420 has only three molded components: the hull, the deck, and the mast partners. Unlike the C420, the Z420 does not include a spinnaker or trapeze in its rigging. Z420 boats are specially designed for college sailing and were used at the Inter-Collegiate Sailing Association National Championships in 2014 for the first time.^[7]