Reflecting an exploding interest, in performance measurement, various state, federal, and commercial entities are calling for public reporting on hospital quality. A number of measures are currently being developed or tested. Lacking, however, is a consensus about the properform and function of health care quality measures. This essay is a contribution to the growing dialog on the utility, practicality, and target audience of various measures. All measures have a subject (what they measure) and a function (the use or purpose of the measures). Subject measures shed light on process (activities prior to, and during care) or outcome (the intended or unintended result of care). Measures also fill 2 different functions: Quality improvement measures are more detailed and are designed for continuous internal consumption. Accountability measures ("report cards") are designed for external consumption, are typically shorter, less frequently generated, and reported at the hospital or clinic level. It is important that the 2 functions not be confused in constructing and targeting future quality measures.