In this analysis of the global workforce, the Joint Learning Initiative, a consortium of more than 100 health leaders, proposes that mobilization and strengthening of human resources for health, neglected yet critical, is central to combating health crises in some of the world's poorest countries and for building sustainable health systems everywhere. Worker shortage, skill mix imbalance, maldistribution, negative work environments, and weak knowledge bases challenge nearly all countries. Especially in the poorest countries, the workforce is under assault by a triple threat of HIV/AIDS, out-migration, and inadequate investment. Effective country strategies should be launched and backed by international reinforcement. These include urgently mobilizing one million more health workers for Africa, and focusing efforts on the unremunerated community-level health workers, the majority of whom are women. Ultimately, the crisis in human resources is a shared problem requiring shared responsibility for cooperative action. Alliances for action are recommended to strengthen the performance of all actors while expanding space and energy for new ones.