The role of the private sector in public healthcare systems is much debated, but there is little research to inform the debate. In the Nordic countries the extent and type of private sector involvement is largely unknown and the changes and the consequences have not been studied. This paper presents a conceptual framework and some limited data about the changing private-public mix and privatization in the Nordic countries between 1985 and 2000. The data suggest a small increase in both private financing and provision which has accelerated in recent years, especially in specific healthcare fields such as diagnostic centres, dentistry, primary medical care and care for older people. The overall increase is small, but large in certain sectors. Differences between the countries can only be understood in relation to their historical, financial, economic and political context, even though there are many commonalities. Impact also is context dependent, but the findings do show a cross-country pattern of a willingness to experiment and a change in underlying assumptions. The findings show a more extensive interpenetration of private and public than previously recognized but more research is required, especially about changes in recent years about which data are scarce. The paper considers the factors driving these trends, the likely larger changes in the next 10 years and the possible consequences for patients, professionals, managers and governments. It notes the different ways governments can control or influence finance and provision. It proposes that the Nordic and other governments improve regulation and data collection about the private sector and consider influencing private providers through partnership arrangements, rather than leaving the developments to be shaped by growing consumer demands or market logic alone.