Increasing competitive pressure from global markets and technological developments has resulted in the continual demand for business improvement philosophies and methodologies in operations management to address this challenge. The Six Sigma approach to business improvement has emerged in both the practitioner and academic literature as having a significant role in this area. There are many documented case studies of organizational applications of Six Sigma, where largescale improvements in defect and process measures have been attributed to this approach, mainly in the massmanufacturing sector. Moreover, there are claims, less well documented, that Six Sigma can be used as a change management approach at a strategic level and thus it can be applied to other sectors such as service industries. It is contended that there is a paucity of critical reviews of the Six Sigma literature, beyond that of descriptive accounts. Therefore, the aim of this paper is to critically review the literature of Six Sigma in relation to its effect on organizations and those that work in them. A broad theoretical perspective is used to guide the review process. The paper structure is based on the dichotomies within the Six Sigma literature, namely, what is Six Sigma — strategic change or operational methods; is Six Sigma a TQM appendage, or something new; will workers in a Six Sigma environment have more empowerment or be more controlled and is Six Sigma applicable to the service sector or only for that of the manufacturing sector?