Arch expansion is a method of gaining space. An apparently complex yet relatively simple procedure in orthodontics is Palatal expansion. The correction of transverse maxillary deficiency can be an important component of an orthodontic treatment plan. Rapid Maxillary expansion (RME) is a skeletal type of expansion that involves the separation of the mid-palatal suture and movement of the maxillary shelves away from each other. RME effects the maxillary complex, palatal vaults, maxillary anterior and posterior teeth, adjacent periodontal structures to bring about an expansion in the maxillary arch. The majority of dental transverse measurements changed significantly as a result of RME. This review article provides detailed information about rapid maxillary expansion and the appliances used commonly for RME.