Dressage (/ˈdrɛsɑːʒ/ or /drɪˈsɑːʒ/; French: [dʁɛsaʒ], most commonly translated as "training") is a form of horse riding performed in exhibition and competition, as well as an art sometimes pursued solely for the sake of mastery. As an equestrian sport defined by the International Equestrian Federation, dressage is described as "the highest expression of horse training" where "horse and rider are expected to perform from memory a series of predetermined movements".

Competitions are held at all levels from amateur to the Olympic Games and World Equestrian Games. Its fundamental purpose is to develop, through standardized progressive training methods, a horse's natural athletic ability and willingness to perform, thereby maximizing its potential as a riding horse. At the peak of a dressage horse's gymnastic development, the horse responds smoothly to a skilled rider's minimal aids. The rider is relaxed and appears effort-free while the horse willingly performs the requested movement.

The discipline has a rich history with ancient roots in the writings of Xenophon. Modern dressage has evolved as an important equestrian pursuit since the Renaissance when Federico Grisone's "The Rules of Riding" was published in 1550, one of the first notable European treatises on equitation since Xenophon's On Horsemanship. Much about training systems used today reflects practices of classical dressage.

In modern dressage competition, successful training at the various levels is demonstrated through the performance of "tests", prescribed series of movements ridden within a standard arena. Judges evaluate each movement on the basis of a standard appropriate to the level of the test and assign each movement a score from zero to ten – zero being "not executed" and 10 being "excellent". A competitor achieving all 6s (or 60% overall) might typically then move up to the next level.

The most popular horse breeds seen at the Olympics and other international FEI competitions are warmblood horses bred for dressage.

In classical dressage training and performances that involve the "airs above the ground" (described below), the "baroque" breeds of horses are popular and purposely bred for these specialties.

There are two sizes of arenas, small and standard. Each has letters assigned to positions around the arena for dressage tests to specify where movements are to be performed. Cones with letters on them are positioned on the sidelines of the arena for reference as to where a movement is to be performed.

The small arena is 20 by 40 m (66 by 131 ft) and is used for the lower levels of eventing in the dressage phase, as well as for some pure dressage competitions at lower levels. Its letters around the outside edge, starting from the point of entry and moving clockwise, are A-K-E-H-C-M-B-F. Letters also mark locations along the "center line" in the middle of the arena. Moving down the center line from A, they are D-X-G, with X being directly between E and B.