This document is the consensus view of the Calibrated Leak Subcommittee of the Recommended Practices Committee of the American Vacuum Society. It is divided into four main sections: Description, Calibration, Proper Usage, and Recommended Documentation of Leaks. Included in Sec. II are discussions of types of leaks, temperature effects, depletion rates, and units of leakage rate measurement. Section III addresses primary and secondary techniques for leak calibration, including uncertainties. Section IV addresses the proper handling and usage of leaks to achieve optimum results, recommendations of standardization of connections, and safety. The documentation to accompany and to be attached to each calibrated leak, recommended in Sec. V, is intended to provide the user with sufficient information about the leak for accurate and safe use. The appendices contain a glossary and a discussion of the use of throughput and flow rate units and conversions.