The main aim of this volume is to provide an updated overview of the genetic basis of a group of complex disorders that are considered rare individually, but show a relatively high prevalence on the whole in developed countries: the rare autoimmune diseases. These are chronic disorders that involve long and expensive treatments with considerable side effects that may dramatically reduce the quality of life of affected people. Therefore, shedding light into their pathologic mechanisms is a major concern given their growing social and economic awareness and impact.General sections include different chapters on single entities as systemic lupus and sclerosis, Behçets disease, Sjogrens syndrome and polymiositis, and sections devoted to autoimmune vasculitis, hepatic autoimmune conditions, as well as those affecting the nervous system, and a concluding chapter in which the shared predisposition amongst all diseases is discussed. All the chapters are given a homogeneous scheme in which the authors explain the clinical singularities of every disease and report the recent breakthrough discoveries related to them, giving a critical interpretation and suggesting future perspectives. All contributors are renowned researchers with high expertise in each disease. Due to the exponential increase in our understanding of the genetic causes of these complex diseases, a major advance in biomedical discovery is taking place. However, most of the achievements in this field are very recent and there is a lack of bibliography gathering them together. This book is thus filling a gap and will prove a useful companion to clinicians in the first place (internists, rheumatologists, clinical immunologists, and hematologists) but also to basic and applied researchers.