The delivery of an appropriate quantity and quality of health care in an efficient way requires, among other things, matching the supply with the demand for the services of physicians, over time. Such matching has led to very different levels of physicians per million population across OECD countries--because of variations, among other things, in: morbidity and mortality, health expenditure as a share of GDP and the design of health systems. In addition, there are signs that a higher density of physicians is found in countries which have left the supply of physicians mainly to the market whereas lower density is found in countries which have planned the intake to medical schools centrally over many years. Shortages of physicians have now appeared in a number of OECD countries. It seems likely that these shortages could worsen in some countries over the next two decades, as a result of rising demand for, and falling supply of, physicians, unless countermeasures are taken quickly. The countermeasures may involve recruiting into medicine a higher proportion of dwindling cohorts of young people which is likely, in turn, to require raising the relative pay of physicians and/or improving their conditions of service. Countries have at their disposal a variety of additional policy instruments to influence the supply of physicians including education and training policies, migration policies and policies affecting retention and retirement. A number of countries are now raising their intake to medical schools, or discussing raising it. Immigration of doctors can ease physician shortages in countries where numbers are lacking but it raises difficult questions about international equity when there are net, long-term flows of physicians from poorer countries with low average health status to richer countries with high health status. As a result, many OECD countries aim for self-sufficiency in physician supply. Against expectations of a wave of retirement of physicians in many OECD countries, several countries are trying to tempt physicians into delaying their retirement by making retirement arrangements more flexible and staying longer in practice more rewarding, financially. Most OECD countries experience inequities in the geographical distribution of their physician workforce. To tackle this difficulty, a mix of educational policies, regulatory policies and financial policies has been used with some success in a number of countries. Against increasing trends towards specialisation, some countries are trying to raise the relative attractiveness of careers in primary care. There is some evidence to suggest that giving students experience of primary care practice and appointing primary-care role models to academic positions, can influence students' choices towards a career in primary care. The services delivered by physicians depend on their productivity as well as on their numbers. There is good evidence that activity-related methods of payment will raise the activity rates of physicians, but this is also likely to raise costs and little is known about the effect that raised activity has on quality of care. There is growing interest in devising payment systems for physicians which reward the quality of care directly--where that is feasible. (Contains 12 footnotes, 13 figures, 6 boxes and 5 tables.)