In comparative studies of health care, the United Kingdom's health care system continues to be categorized in terms of public finance and public provision. However, over 11% of the United Kingdom population has private medical insurance (PMI), and PMI is an important contributor to the United Kingdom's health economy (the market being worth almost 3 billion a year). This study provides an introductory overview of an often-ignored and significantly under-researched area.The study is structured according to the three key dimensions of the market for PMI: the product, demand and supply. It also includes a short appendix on the market for health cash plans--an alternative form of private cover for medical expenses with relatively broad take-up. The Introduction provides a classification of forms of voluntary health insurance (VHI) and locates PMI within the wider United Kingdom health care system."