In the past three decades, not much has changed in the pathophysiologic concepts of dermatomyositis and polymyositis. However, in the past couple of years, many changes have occurred reflecting the extremely complex nature of the immune response in general. New pathophysiologic models are needed, but at present, none of them encompasses all the recent findings. The changing concepts of dermatomyositis and polymyositis offer new opportunities for unraveling these diseases and developing better strategies for prevention and treatment. This article discusses the most important developments and their methodologic short-comings.