The necessity of measurement.

Measurement of library systems and services is a multidimensional management task. New paradigms of library service and the context in which libraries operate have made it necessary for librarians to find new measures while at the same time keeping the old. Factors that can be measured, such as needs, inputs, quality processes, outputs, quality of service, outcomes, and impacts, are described. This bibliographic essay covers the current trends while leading readers to resources where they can learn more.