Recently, there has been an expansion of different forms of systematic review of research and the development of guidance and standards about particular types of review. These reviews can be best understood within a broad framework of the dimensions on which reviews differ, and how the review methodology relates to the methodology of primary research. Similarly, publication standards can be understood in terms of their relation to other standards such as guidance and rules for undertaking reviews and systems for appraising the quality of reviews. This commentary is written with special reference to the publication standards for meta-narrative and realist reviews being published in BMC Medicine.See related research articles http://www.biomedcentral.com/1741-7015/11/20 and http://www.biomedcentral.com/1741-7015/11/21.