The Medical Outcomes Trust is a depository and distributor of high-quality, standardized, health outcomes measurement instruments to national and international health communities. Every instrument in the Trust library is reviewed by the Scientific Advisory Committee against a rigorous set of eight attributes. These attributes consist of the following: (1) conceptual and measurement model; (2) reliability; (3) validity; (4) responsiveness; (5) interpretability; (6) respondent and administrative burden; (7) alternative forms; and (8) cultural and language adaptations. In addition to a full description of each attribute, we discuss uses of these criteria beyond evaluation of existing instruments and lessons learned in the first few rounds of instrument review against these criteria.