The number of health workers employed is an indicator of a country’s ability to meet the health care needs of its people, especially the poorest and most vulnerable. Resource-constrained countries committed to the Millennium Development Goals are facing up to the reality that shortages and uneven distribution of health workers threaten their capacity to tackle the HIV/AIDS pandemic, as well as the resurgence of tuberculosis and malaria. Worker shortages are linked to three factors: 1) decreasing student enrollment in health training institutions, 2) delays or freezes in the hiring of qualified professionals and 3) high turnover among those already employed. Increasingly, health care managers and organizations are focusing attention on the problem of low retention, recognizing that these losses are costly, negatively effect continuity of care and raise the potential for turnover of remaining employees who suffer stress and burnout from taking on the additional burden of care. Based on an intensive literature review, this technical brief considers challenges and responses related to retention of health care workers, including the causes of turnover, actions to address turnover and emerging evidence on retention approaches. The brief considers retention primarily in the context of sub-Saharan Africa.