Investigators from IMACS, PRINTO, EuorMyositis and the University of Pittsburgh are planning to develop new criteria for clinical improvement, as well as criteria for moderate or major clinical responses, for patients with adult and juvenile dermatomyositis and polymyositis. This effort, which has been funded through the American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR), will involve an international multidisciplinary effort to pool the data from multiple clinical studies and therapeutic trials, and involve consensus opinion of myositis expert clinicians participating in these international collaborative groups. These new criteria should be able to be used as therapeutic endpoints for myositis therapeutic trials and clinical studies.