The following article reviews the role of magnetic resonance imaging (MRI) in patients with idiopathic inflammatory myopathies (IIMs), focusing on the 3 major types of IIM: polymyositis, dermatomyositis, and inclusion-body myositis. After a brief introduction with general information about IIM, we will discuss the reasons why MRI plays an important role in the diagnosis and management of patients with polymyositis, dermatomyositis, and inclusion-body myositis. Magnetic resonance imaging can confirm the diagnosis and can help to phenotype the disease. Moreover, the support of MRI is important in addressing the muscle biopsy site and in reducing the high false-negative rate of biopsy when performed in a blind fashion. In monitoring therapy, MRI can add important information about the activity of the muscle disease and can identify cases where continued immunosuppressive therapy is no longer warranted owing to complete fatty replacement of the muscles. Lastly, we provide an overview about some advanced MRI techniques that focus more on function than on morphology of muscle.