The Welsh Heart Programme (Heartbeat Wales) is a national demonstration project established in 1985 to promote good health amongst the three million population of Wales, and specifically to reduce the risks of cardiovascular disease on a total population basis. The evaluation of community-based health promotion programmes creates major challenges for researchers. This paper describes the progress achieved, current plans and future possibilities together with an outline of the programme's intervention framework. Four key evaluation elements are outlined. The first, programme definition, concerns clarification of the specific inputs, activities and projects which in combination form the Welsh Heart Programme. The second, outcome evaluation, includes a description of the survey methodology used in monitoring change in health status and in the supporting environment in Wales, together with approaches for investigating a causal relationship. Thirdly, process evaluation examines the process of change and addresses issues of feasibility, change mechanisms, and assimilation. Finally policy relevance is considered including assessing the relationship between costs and benefits, and the possibilities for replication of component parts of the programme in other areas, setting and time spans.