This paper discusses the work of the EUHPID Project to develop a European Health Promotion Monitoring System based on a common set of health promotion indicators. The Project has established three working groups to progress this task--health promotion policy and practice-driven, data-driven and theory-driven. The work of the latter group is reviewed in particular. EUHPID has taken a systems theory approach in order to develop a model as a common frame of reference and a rational basis for the selection, organization and interpretation of health promotion indicators. After reviewing the strengths and weaknesses of those health promotion models currently proposed for indicator development, the paper proposes a general systems model of health development, and specific analytical, socio-ecological models related to public health and health promotion. These are described and discussed in detail. Taking the Ottawa Charter as the preferred framework for health promotion, the socio-ecological model for health promotion adopts its five action areas to form five types of systems. The structure and processes for each of these five systems are proposed to form the basis of a classification system for health promotion indicators. The paper goes on to illustrate such a system with reference to indicators in the workplace setting. The EUHPID Consortium suggest that their socio-ecological model could become a common reference point for the public health field generally, and offer an invitation to interested readers to contribute to this development.