The Lock Performance Monitoring System (PMS) is a part of the Inland Navigation Systems Analysis (INSA) program and encompasses the collection, editing, maintenance and analysis of data collected at all Corps-owned and operated locks. The data have been collected since March of 1975 and consist of information describing the traffic through the locks as well as the physical aspects of lockages. This report provides an overview of the system. The appendixes describe the information collected and produced, list the locks at which information is recorded, list the commodity codes and provide a brief glossary of terms.