The rein back is a controlled movement where the horse steps backwards in a straight line, one hoof at a time, in a diagonal sequence. It is an exercise that tests the horse's obedience, suppleness, and balance, as moving backwards is not a natural gait. In dressage, the rein back is used to enhance the horse's attentiveness and responsiveness to the rider's aids and to improve its overall balance and coordination.

Key aspects of the rein back include:

Rhythm and Regularity: The movement should be executed in a steady, rhythmic manner, with the horse's legs moving back in clear, diagonal pairs (right hind with left front, and left hind with right front).

Straightness: The horse should move directly backward without drifting sideways. The rider must ensure that the aids are applied evenly to maintain this straightness.

Softness: The horse should not resist the rider's cues but instead move back willingly, maintaining a soft and relaxed posture throughout the movement.