A comprehensive framework for conceptualizing irrigation performance is presented which, by clarifying relationships among the many incommensurate approaches to performance assessments, can provide the basis for more systematic comparative assessments of irrigation. Irrigation systems are carefully defined, and their relationships to broader agricultural and socioeconomic systems specified in terms both of goals and of inputs and outputs. Goals are seen as crucial to performance assessments, and the existence of many sometimes conflicting goals requires both specification of whose goals are being considered and clarification as to whether the goals are related to inputs, to outputs or to efficiency. Assessments can be categorized according to their purpose, with significant differences among those that monitor operational performance, those that facilitate interventions to improve performance, and those that promote accountability within an operating agency. Assessments also differ in the types of performance measures used. Three distinct categories of performance measures are identified: process measures, which relate to a system's internal operations; output measures, which focus on a system's final output; and impact measures, which pertain to the effects that the system's outputs induce in its larger environment. Performance measures are distinguished from performance standards which may be established from a variety of sources.