During the past 10 years, community health workers (CHWs) have emerged as a focal point of international discussions of primary health-care systems. Although lay community-based health workers have been active for at least 60 years, the Millennium Development Goals (MDGs) in 2000 prompted new discussion of how these workers can help to extend primary health care from facilities to communities. CHWs have since been part of an international attempt to revise primary health-care delivery in low-income settings, and CHW programmes have been changed accordingly. Instead of being regarded as unpaid, lightly trained members of the community who focus mainly on health education and provide basic treatments, CHWs are increasingly envisioned as a trained and paid corps who give advice and treatments, and implement preventive measures. Many national governments, including those of Brazil, Pakistan, Ethiopia, and India, are making CHWs a cornerstone of the scaling up of community health delivery.