We provide a 'how to' guide to undertake systematic reviews of effects in international development, by which we mean, synthesis of literature relating to the effectiveness of particular development interventions. Our remit includes determining the review's questions and scope, literature search, critical appraisal, methods of synthesis including meta-analysis, and assessing the extent to which generalisable conclusions can be drawn using a theory-based approach. Our work draws on the experiences of the International Initiative for Impact Evaluation's (3ie's) systematic reviews programme. © 2012 Copyright 2012 Hugh Waddington, Howard White, Birte Snilstveit, Jorge Garcia Hombrados, Martina Vojtkova, Philip Davies, Ami Bhavsar, John Eyers, Tracey Perez Koehlmoos, Mark Petticrew, Jeffrey C. Valentine, Peter Tugwell.