Upper extremity composite tissue defects may result from trauma, tumor resection, infection, or congenital malformations. When reconstructing these defects the ultimate objectives are to provide adequate soft tissue protection of vital structures, and to provide optimal functional and esthetic outcomes. The development of clinical microsurgery has added a large number of treatment options to the trauma surgeon's armamentarium - primarily replantation of amputated tissues and transplantation of vascularized tissues from distant donor sites. Since the early 1970s, considerable refinement in microsurgical tools and techniques together with a better understanding of the anatomy and physiology of microcirculatory tissue perfusion led to the introduction of a variety of thin, pliable and versatile-free flap designs. Sources for this manuscript include a comprehensive literature search using the PUBMED and EMBASE databases along with relevant text books, Selected Readings in Plastic Surgery(®), and personal experiences of upper extremity reconstruction and microsurgery. In this manuscript, we describe the primary microsurgical techniques used to reconstruct upper extremity tissue defects and discuss the basis for selecting one technique over another. Where possible, the best results may be achieved by reattaching the amputated original tissues (microsurgical replantation). In noninfected, uncontaminated traumatic injuries resulting in composite soft tissue defects, Early free flap reconstruction of the upper extremities has important advantages over delayed (72 h-3 months) or late wound closure (3 months-2 years). In recent years, thin, pliable, and versatile fasciocutaneous flaps such as the anterolateral thigh (ALT) and lateral arm (LA) free flaps have been increasingly used with great success to reconstruct the upper extremity. The use of "spare parts" and functional reconstructions using osteomyocutaneous free flaps or toe to thumb transfers complete the armamentarium of the upper limb reconstructive microsurgeon.