This review looks at the many different factors thought to play a role in idiopathic inflammatory myopathies (IIM), concentrating mainly on the dermatomyositis (DM) subtype. Subject areas addressed include looking at the different clinical features of IIM, paying particular attention to the skin manifestations. There is a discussion around investigations needed with their perceived value, followed by a description of the immunohistochemical findings of DM. This review goes on to address other attributing factors such as genetic associations with the different subtypes of IIM, and environmental factors including infections, ultraviolet radiation and vitamin D deficiency and drugs. Finally, the potential immunopathogenesis of DM is summarized, looking at T cells, B cells, autoantibodies, dendritic cells, cytokines and nonimmune-mediated endoplasmic reticulum stress.