Idiopathic inflammatory myopathies are a heterogeneous group of muscle disorders characterized by chronic muscle inflammation and progressive muscle weakness. Polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM) are the three major subsets based on distinct clinical and histopathological features. Since the pathogenesis remains unclear, therapeutic approaches actually comprise unspecific immunosuppressive strategies with limited success and frequent side effects. Therefore, a deeper understanding of the underlying pathophysiological mechanisms is critically required to develop targeted therapies.