Last summer, the StudentCouncil of the InternationalSociety for Computational Biology prompted an Editorial, ‘‘Ten

[1]. The interest in that piece (it has been downloaded 14,880 times thus far) prompted ‘‘Ten Simple Rules for Writing a Grant’ ’ [2]. With this third contribution, the ‘‘Ten Rules’ ’ series would seem to be established, and more rules for different audiences are in the making. Ten Simple Rules for Reviewers is based upon our years of experience as reviewers and as managers of the review process. Suggestions also came from PLoS staff and Editors and our research groups, the latter being new and fresh to the process of reviewing. The rules for getting articles published included advice on becoming a reviewer early in your career. If you followed that advice, by working through your mentors who will ask you to review, you will then hopefully find these Ten Rules for Reviewers helpful. There is no magic formula for what constitutes a good or a bad paper—the majority of papers fall in between—so what do you look for as a reviewer? We would suggest, above all else, you are looking for what the journal you are reviewing for prides itself on. Scientific novelty— there is just too much ‘‘me-too’ ’ in scientific papers—is often the prerequisite, but not always. There is certainly a place for papers that, for example, support existing hypotheses, or provide a new or modified interpretation of an existing finding. After journal scope, it comes down to a well-presented argument and everything else described in ‘‘Ten Simple Rules for Getting Published’’ [1]. Once you know what to look for in a paper, the following simple reviewer guidelines we hope will be useful. Certainly (as with all PLoS Computational Biology material) we invite readers to use the PLoS eLetters feature to suggest their own rules and comments on this important subject