Although Six Sigma has been of importance to industry for a number of years, the academic community has been slower to study this phenomenon. However there has been a recent increase in the number of published papers in more academic journals, particularly from 2000 onwards. It is therefore a timely point at which to extensively review the literature on Six Sigma and to identify the key academic studies that have been undertaken. This paper reviews more than 200 papers, classifying them according to their research content and the research methodology employed. A comprehensive list of future research areas is given. Key examples are further development of a scientific foundation for the methodology; integrating Six Sigma with other methodologies such as adding Lean Tools; considering implementation issues in areas other than North America & Europe and furthering the debate on how to adapt the approach for use in a service context.