The Climate Change Science Program (CCSP) and its predecessor U.S. Global Change Research Program have sponsored climate research and observations for nearly 15 years, yet the overall progress of the program has not been measured systematically. MetricsaEURO"a system of measurement that includes the item being measured, the unit of measurement, and the value of the unitaEURO"offer a tool for measuring such progress; improving program performance; and demonstrating program successes to Congress, the Office of Management and Budget, and the public. This report lays out a framework for creating and implementing metrics for the CCSP. A general set of metrics provides a starting point for identifying the most important measures, and the principles provide guidance for refining the metrics and avoiding unintended consequences.