Codvilla first developed tissue expansion in 1905 through the application of an external fixation device that successfully showed the ability to elongate bone through distraction forces. Reconstruction evolved to extrapolate this concept to promote the lengthening of skin and soft tissues by Putti in 1950 and was then applied to reconstructive surgery through an implantable device by Neumann in ear reconstruction. Tissue expansion provides a safe and reliable method of reconstruction for extensive soft tissue defects. This chapter aims to describe the purpose of tissue expansion and the key physiologic mechanism and relevant anatomy that contribute to this process (Codivilla, JBJS 2:353–369, 1905; Putti and Peltier, Clin Orthop Relat Res 250:4–7, 1990; Radovan, Plast Reconstr Surg 74:482–492, 1984).