Expansion is a tempting means of gaining space with the added advantage of being a conservative procedure. Expansion can be done in transverse direction, sagittal direction or a combination. Debate is on, regarding the stability and progress of expansion since the day the theory of expansion has been put forward. Despite this, considerable success has been achieved by expansion. With patient cooperation, expansion of the dental arches especially during the mixed dentition period has yielded good result. As with any form of therapy there are contraindications, occasional unfavorable responses and at times partial success. Nevertheless when properly used, expansion is of great value in treating malocclusion. Success of the treatment is measured not only by the proper functional occlusion that is achieved along with improved appearance of the patients but also by long term stability of the results obtained. This book will focus in brief on arena of expansion in orthodontics.