Health financing policies are marked by confusion between policy tools and policy objectives, especially in low and middle income countries. This paper attempts to address this problem by providing a conceptual framework that is driven by the normative objective of enhancing the 'insurance function' (access to needed care without financial impoverishment) of health care systems. The framework is proposed as a tool for descriptive analysis of the key functions, policies, and interactions within an existing health care system, and equally as a tool to assist the identification and preliminary assessment of policy options. The aim is to help to clarify the policy levers that are available to enhance the insurance function for the population as efficiently as possible, given the 'starting point' of a country's existing institutional and organizational arrangements. Analysis of health care financing systems using this framework highlights the interactions of various policies and the need for a coherent package of coordinated reforms, rather than a focus on particular organizational forms of 'health insurance'. The content of each main health care system function (revenue collection, pooling of funds, purchasing of services, provision of services) and the market structure with which the implementation of each is organized are found to be particularly important, as are policies with respect to the benefit package and user fees.