Expansion is a tempting means of gaining space, and it has been stated that crowding is due to posterior crossbite that develops early and is not self-correcting. Angle described the first use of rapid maxillary expansion (RME) in 1860, and he taught that the ideal occlusion can be achieved when all teeth are accommodated in the dental arch to get a functional efficiency and to ensure a permanent result. Since reduced transverse dimension can also be an etiologic factor for the development of arch length discrepancies, expansion can be used for alleviating the crowding in selective cases. In RME, the dental and skeletal effects have been well documented, for correcting maxillary alveolar constriction. The expansion appliances can be classified into removable, semi-fixed, or fixed appliances, and based on the mode of activation, it can be either slow or rapid. The objective of this article is to create a better understanding of expansion as an important part of orthodontic treatment modality which can be a very valid solution to many space problems during treatment, as it is one of the most frequently used methods of gaining space.