Retention is the phase of orthodontic treatment which maintains the teeth in their orthodontically corrected positions following the cessation of active orthodontic tooth movement. Orthodontic retainers resist the tendency of teeth to return to their pre-treatment positions under the influence of periodontal, occlusal and soft tissue forces, and continuing dentofacial growth. Very few prospective controlled studies have evaluated the effectiveness of retention. In addition, very little is known about patient's perception in relation to orthodontic relapse. Various studies have shown that fixed retention bonded only to canines have relapse, while others have shown that even though relapse exists, it is not significant or clinically relevant. This book summarize about each aspect of relapse and retention.