This book develops and describes surgical rationales in the field of reconstructive surgery for upper limb function, both in children and adults suffering from various diseases or trauma leading to a variety of motor and sensory impairments, sometimes associated with growth-related deformities. Every surgical career is a unique living story of learning, performing, questioning, trial and error, and finally success. Every surgeon has to integrate a wealth of information regarding ongoing clinical and research work in a range of disciplines; and with time and experience, a surgical rationale is developed that serves as a baseline and support for their day-to-day work. Following a structure starting with the patient’s needs, the surgeon and the training, the different tissues are addressed and their pathophysiology discussed in detail, including basic research and surgical expertise. The book is not a surgical compendium, but instead focuses on the detailed baseline behind day-to-day clinical examinations, functional evaluations and surgical work. Readers will learn how the tissues interact, how pathologies change them and interfere with their functions, and how to reverse the pathophysiological sequence by surgical-technical means to improve function. Although the book presents the author’s personal views, all aspects are explained and debated on the basis of past and current clinical findings, ongoing basic research and input from other disciplines: readers may disagree with certain points, but choose to implement some of the rationales and priorities, incorporate findings from fields they’d never previously explored, or investigate them further. This book offers an extensive framework of argumentation and is intended to inspire and support readers in terms of decision-making and understanding current or uncommon procedures. Practitioners in the fields of peripheral nerve surgery, reconstructive plastic surgery, upper limb orthopedics, neuropediactrics, biomechanics, physiotherapy and ergotherapy will find the book a valuable asset, and a trusted companion in the daily quest to improve patient care!