The document is one of five training modules developed by the Office of Water Enforcement and Permits, U.S. Environmental Protection Agency to introduce the National Pollutant Discharge Elimination System (NPDES) program to new inspectors. This module has been organized to highlight the major components involved in a laboratory evaluation conducted as part of a CEI, (Compliance Evaluation Inspection) and in a more comprehensive laboratory evaluation conducted during a PAI (Performance Audit Inspection). The module discusses the following subjects for the two types of inspections: Performance Audit Inspection--(completing preinspection planning, conducting the initial meeting, observing sampling techniques, assessing the laboratory's sample control, reviewing the laboratory's analytical methods, evaluating the laboratory's Quality Assurance/Quality Control (QA/QC) techniques, reviewing the laboratory's Discharge Monitoring Reports (DMR) QA lab data and records, conducting an audit of the laboratory's facilities and equipment, conducting the exit meeting, and preparing the final report). Compliance Evaluation Inspection--(reviewing records and reports, completing a review of self-monitoring data and procedures, and conducting a review of the laboratory facilities). The objective of the module is to provide the inspector with background information necessary to conduct an appropriate evaluation of the permittee's laboratory procedures for sample control, sample analysis, and quality assurance, as well as to assess the adequacy of the laboratory facilities and equipment. Additional sources of information are provided in the references identified throughout the text of the module and summarized in Appendix A. A glossary of terms used in the module appears as Appendix B.