Background: While much of the world struggles with having too little to eat, in the west, obesity has emerged as an important (sometimes described as the most important) public health issue. This paper describes a suite of studies carried out at the EPPI-Centre, Institute of Education, University of London, and the challenges of synthesizing the findings from diverse studies and other forms of evidence. In 2008, the EPPI-Centre began work on a new programme of systematic reviews for the English Department of Health. These cover social and environmental interventions in promoting positive behaviours for healthy weight; have described and mapped schemes set up to tackle overweight and obesity in children; includes a review of views, and has looked at the research evidence on the relationship between obesity and attainment. Our work liaising with children and young people has two aims: to identify priorities for interventions (from the views’ review) and narrowing the focus from a map to a full in-depth review. Objectives: Given the growing volume of effectiveness reviews on obesity, our task for policy makers has been to cover some of ’what’s left’ and to make the most of what we know. The objective of this paper is to describe how we did so. Methods: Contributing to existing work in building up a comprehensive evidence base takes us into new territory. The methods we have used include ’mapping’; creating a database; systematic reviewing; consulting young people and synthesis. Results: This work has resulted in systematic reviews, a searchable database and recommendations from young people and those who work with them in schools on what needs to be prioritised. Conclusions: We will describe how mapping and consultations have affected the direction and uses of the review.