Against this background, the objective of this project was to gather and assess the extent of available evidence on the economic efficiency of population health interventions as the first step in a program of work designed eventually to assess the value of investing in population health. [...] At this stage, eligible references were also classified according to a four-part typology reporting the strategic focus of the intervention (as defined by the WHO), the risk factor being targeted, the population most affected and the setting in which the intervention took place. [...] The quality of this evidence varies in terms of the study designs employed to demonstrate effectiveness, the comprehensiveness with which important costs and effects have been included and the validity of the conclusions drawn by study authors. [...] The Census therefore documents the availability of evidence and provides the foundation from which to plan the next steps in the program of work. [...] This included searches of two registries of gray literature, one maintained by the New York Academy of Medicine8 and the second maintained by the University of Laval,9 as well as the web sites of the best-known university- based, health economics research units.