Over the recent decades, notable progress has been made in the understanding of the pathomechanism of autoimmune myositis. Dermatomyositis is considered a type I interferonopathy, distinctive from antisynthetase syndrome despite some common clinical features. Immune-mediated necrotizing myopathy is related to complement-mediated autoimmunity. In inclusion body myositis, myofiber invasion by highly differentiated cytotoxic T cells leads to myofiber damage. Based on the accumulated knowledge, targeted, more mechanism-focused therapies are being developed.