Publisher Summary This chapter discusses clinical trials in muscle disorders. It focuses on the three main areas of muscle diseases in which clinical trials have been or are being performed: (1) autoimmune ion channel disorders, (2) inflammatory myopathies, and (3) primary hereditary myopathies. A group of autoimmune disorders shares a common pathogenesis, mediated by autoantibodies against different ion channels of motor nerve terminals. Myasthenia gravis (MG) and Lambert–Eaton myasthenic syndrome (LEMS) are because of antibodies to postsynaptic acetylcholine receptors (AChRs) and presynaptic voltage-gated calcium channels, respectively. Antibodies against voltage-gated potassium channels have been reported in acquired neuromyotonia. MG is the most commonly observed disease in this group. Its natural course has been modified by the introduction of immunosuppressive drugs and thymectomy. According to the features and severity of the disease, and due to ethical reasons, treatments available for MG have been rarely evaluated in a controlled fashion. Inflammatory myopathies (IM) encompass a heterogenous group of disorders in which clinical, histopathologic, and laboratory data define three major entities: polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM). Although several clinical features are shared by the different forms, pathogenetic mechanisms differ considerably among PM, DM, and IBM. Several disorders mentioned in this chapter may be subdivided into the following categories: (1) muscular dystrophies, (2) congenital myopathies, and (3) myotonic syndromes. The chapter focuses on the main diseases for which a major effort has been expended to perform clinical trials: the Xp21-linked muscular dystrophies (DMD or Becker muscular dystrophies [BMD]), facioscapulohumeral muscular dystrophy (FSHD), and myotonic dystrophy (MD).