Through the recent efforts of multi-center collaborative study groups, a number of measures have been developed and partially validated to assess disease activity, disease damage, and health-related quality of life in adult and juvenile patients with IIM. Preliminary core set domains and core set measures of activity and damage have also been developed for adult and juvenile patients with myositis. Validated definitions of improvement and disability should be forthcoming in the next few years. These extraordinary developments will enable much-needed standardization in the assessment of the IIM, particularly in therapeutic and other clinical research studies. Despite this substantial progress, there is a need to develop more sensitive measures to assess IIM disease activity and damage, to further validate the existing tools, to define their performance characteristics in various IIM subgroups, to develop improved imaging techniques that are also quantitative, and to validate activation markers as surrogate measures. The ongoing cooperation of multiple specialists with expertise in these disorders, combined with emerging novel technologies, should continue to enhance the assessment of myositis. Improved clinical care and more rapid development of new therapies for patients with myositis will be the ultimate gains realized from these efforts.