Conventional methods to identify anaerobic bacteria have often relied on unique clinical findings, isolation of organisms, and laboratory identification by morphology and biochemical tests (phenotypic tests). Although these methods are still fundamental, there is an increasing move toward molecular diagnostics of anaerobes. In this review, some of the molecular approaches to anaerobic diagnostics based on the polymerase chain reaction (PCR) are discussed. This includes several technological advances in PCR-based methods for the detection, identification, and quantitation of anaerobes including real-time PCR which has been successfully used to provide rapid, quantitative data on anaerobic species on clinical samples. Since its introduction in the mid-1980s, PCR has provided many molecular diagnostic tools, some of which are discussed within this review. With the advances in micro-array technology and real-time PCR methods, the future is bright for the development of accurate, quantitative diagnostic tools that can provide information not only on individual anaerobic species but also on whole communities.