In spite of their relatively low prevalence, systemic vasculitides have been the object of intensive basic and clinical investigations over the last few years. As a consequence, important advancements have been achieved: from updated diagnostic and classification criteria and a more rational nomenclature to the recognition of an expanding spectrum of clinical manifestations and potentially devastating complications; from the recognition of the viral etiology of conditions such as HCV-related cryoglobulinemic vasculitis and HBV-associated polyarteritis nodosa to newly named variable vessel vasculitis exemplified by Behçet’s disease; from single-organ vasculitis such as central nervous system vasculitis to the more recently emerging features of the IgG4-related, immune-mediated diseases that are showing remarkable clinical heterogeneity. In addition, intriguing pathogenetic hypotheses are being reported for certain chronic, relapsing vasculitides that are improving our understanding of their biology and basic pathophysiology. New avenues are being explored that will hopefully allow a deeper comprehension of the relationships between certain virus-driven vasculitides and lymphoproliferation, and possibly lead to the identification of novel biomarkers that may be used to single out patients at an increased risk of relapse. This explosion of knowledge is obviously resulting in state-of-the-art, personalized treatments of systemic vasculitides. This book is a collection of reviews on the major vasculitides, written by scientists and clinicians with a multi-year experience in this field. We hope it will provide the reader with a stimulating container of new advances in scientific knowledge and more rational therapeutic approaches to this fascinating chapter of pathology.