The 4 × 400 metres relay or long relay is an athletics track event in which teams consist of four runners who each complete 400 metres or one lap. It is traditionally the final event of a track meet. At top class events, the first leg and the first bend of the second leg are run in lanes. Start lines are thus staggered over a greater distance than in an individual 400 metres race; the runners then typically move to the inside of the track. The slightly longer 4 × 440 yards relay, on an Imperial distance, was a formerly run British Commonwealth and American event, until metrication was completed in the 1970s.

A relay race is a racing competition where members of a team take turns completing parts of racecourse or performing a certain action. Relay races take the form of professional races and amateur games. Relay races are common in running, orienteering, swimming, cross-country skiing, biathlon, or ice skating. In the Olympic Games, there are several types of relay races that are part of track and field. Relay race, also called Relay, is a track-and-field sport consisting of a set number of stages (legs), usually four, each leg run by different members of a team. The runner finishing one leg is usually required to pass the next runner a stick-like object known as a "baton" while both are running in a marked exchange zone. In most relays, team members cover equal distances: Olympic events for both men and women are the 400-metre and 1,600-metre relays. Some non-Olympic relays are held at distances of 800 m, 3,200 m, and 6,000 m. In the less frequently run medley relays, however, the athletes cover different distances in a prescribed order—as in a sprint medley of 200, 200, 400, 800 metres or a distance medley of 1,200, 400, 800, 1,600 metres.