Book excerpt: Polymyositis and Dermatomyositis provides extensive information regarding Polymyositis and Dermatomyositis (PM/DM), which is described as a heterogeneous disease complex. This book is divided into four sections: Part I (Clinical Features) covers the classification of PM/DM, details of the clinical presentation, and the disease's association with the other connective tissue disorders and malignancies. Part II (Etiology and Mechanisms) covers advances in the immunopathology and viral etiology of PM/DM along with a frequently recognized entity: inclusion body myositis. Part III (Diagnosis and Treatment) covers the histologic, muscle enzyme histochemical, electron microscopic, and resin histology features of PM/DM along with those electromyographic features that could help make a more accurate diagnosis. Part IV (Overview) summarizes the issues that may not have been clear and highlights differing and unsettled views or present available data. This text is directed to clinicians in private practice or in academic institutions concerned with PM/DM patients, including neurologists, rheumatologists, pediatricians, dermatologists, physiatrists, and neuromuscular investigators. This book is intended as well for neuromuscular pathologists who interpret muscle biopsy specimens and electromyographers who perform EMG studies to help determine the clinical diagnosis. Researchers in immunology and immunopathology of neuromuscular diseases will find discussions in this book invaluable.