In this article, I survey the economic literature on voluntary insurance and the financing of health care. A first section provides a typology of the variety of financing schemes with their strengths and weaknesses. A second section surveys what we know from a theoretical and empirical perspective on how health care spending can be split between compulsory and voluntary schemes. In that section, I use theoretical results as well as empirical ones drawn from health care systems in Canada, France, the United Kingdom, Switzerland, and the US. The main conclusion is as follows: any pure financing system (i.e., only compulsory or voluntary) will be rejected, both from normative (welfare is lower in a pure system) and positive (no electorate would choose it) perspectives. Mixed systems are therefore not only the result of particular historical circumstances, but rather reflect a rational trade-off between the respective weaknesses of compulsory and voluntary systems.