Health care quality measurement is at least 250 years old. While the names and faces of the measures and measurees have changed, the intent of such measurement, i.e. obtaining data and information bearing clinical outcomes, has not changed over the years, and nor have the challenges associated with the measurement of quality in health care. Measurement is not a neutral activity. It evokes considerable anxiety and frustration among all concerned: those who are being measured, those who are doing the measuring, and those who are seeking the data for a variety of purposes. There is little agreement on the philosophy of measurement, on what to measure, on whether or how to adjust for what the patient brings to the clinical encounter, on how data should be analyzed, or on how to report the data; and of course the ultimate questions relate to the value of measurement. Measurement adds new costs to the health care delivery system. Tangible improvements in care, directly attributable to performance measurement, are repeatedly being documented. However, the jury has not yet returned a verdict on whether performance measurement data are being used by stakeholders for better decision-making.