This chapter describes the process to be followed and the key points to observe when conducting an audit of the microbiology laboratory. An audit is a documented independent inspection and review of a system, which is performed on a periodic basis in accordance with written procedures. The chapter begins with an outline of audits and how they fit into the Quality Management System and then proceeds to examine some of the key functions of the microbiology laboratory. Although the emphasis is upon the quality control pharmaceutical microbiology laboratory, several aspects are applicable to all laboratories.