The world is experiencing a serious human resource shortage in the health sector, which the World Health Assembly calls 'a crisis in health'. This Report systematically explains the human services crisis, particularly in the world's poorest countries. The Report considers the complex mix of factors that cause the global shortage of health workers. We demonstrate why no single country, acting alone, can solve the human resources crisis. In short, a country's health workforce is not determined only by decisions of its national government. Policy choices in one country often have consequences for the health workforce in other countries. We give particular attention to the policy positions of rich countries that contribute to the extreme shortages in much poorer countries. We recommend a range of policy interventions that rich countries, particularly the United States, should make to alleviate workforce shortages domestically and globally. Our recommendations are based on the best-available evidence as to what interventions are most likely to be successful in addressing the causes and consequences of the shortage. They are also predicated on a normative analysis of the legal rights and obligations, as well as moral interests and claims, of governments, health workers, and users of health services.