Six years have already passed since the publication of the first edition of this diagnostic reference. Studies and reports of new autoantibodies and their clinical associations remain a very dynamic field of investigation. A rapid increase of new data regarding novel autoantibodies, the clinical and pathological relevance of autoantibodies, novel diagnostic possibilities as well as new autoimmune disease entities has been published. As examples, a set of agonistic or inhibiting autoantibodies against receptor structures have revealed further insights into autoimmune mechanisms and recently discovered and evaluated autoantibody specificities have led to an appreciation of special autoimmune entities like subtypes of autoimmune encephalopathies, anti-IgLON5-related tauopathy and IgG4-mediated paranodopathy. In addition, novel assays for autoantibody determinations have been developed and adopted into routine diagnostics. Furthermore, novel results of evaluation studies and metaanalyses have lead to a reassessment of the clinical relevances of some autoantibody specificities. All these aspects required an updated and timely completion of this volume to meet the requirements of a comprehensive and useful reference book for the serological diagnosis of autoimmune diseases as well as clinically relevant autoimmune research. We want to thank all mindful and critical readers for their useful feedback since the publication of the last edition.