A useful theory of performance measurement for prosecution and public defense must address the questions of what should be included for measurement, the measures to use, and the purpose of measurement. There are three basic levels of performance for which a measurement theory can be developed in the criminal justice system; individual performance, which focuses on the individual prosecutor or public defender; criminal justice system performance, which focuses on the combined effects of the various components of the system; and agency performance, which focuses on the operations, management, and planning functions of an agency. Basic principles and approaches especially suitable in defining a prosecution or defense agency's activities are that (1) descriptions of the agency's activities should be in terms of their functions, (2) only those factors or activities over which the agency has control and for which it can be held accountable should be included in the measurement schema, and (3) the framework within which the measurement is assessed should be based on agency policy. In addition, performance measurement for an agency must define the agency's outputs, identify the variables that affect the output, and develop measures which can satisfy a variety of purposes. The last component of a theory for performance measurement is the identification of some of its primary uses and the development of measures and measurement concepts that are compatible with these uses. The report discusses the need for performance measures, a functional approach for performance measurement, the dynamics of functional analysis, the structure of decisionmaking systems, and statistical systems for performance measurement. A final chapter considers performance as the delivery of services. Figures and approximately 120 references are provided. An appendix (see NCJ 78801) discusses a composite index of criminality.