The Upper Limb Committee of ESSKA was created in 2007. The goal of this committee is to promote the knowledge of Upper Limb Surgery. Among the activities carried out are Arthroscopic Shoulder Courses, Multicentric studies, meeting sessions. This book is the first publication released by the committee. It focuses attention on the "state of the art" of gleno-humeral instability. The understanding of pathomechanic, clinical evaluation and the different treatment options are changing rapidly, therefore we were happy to present the most updated concept regarding this topic. This book is intended as the first step for future European collective publications, in order to help the surgeons in their clinical practice.