Recently there has been a renewed emphasis on the importance of a well-functioning health system in order to ensure sustainable access to essential health services, including HIV/AIDS. At the same time, there is growing recognition that the private sector plays a key role in the health systems of many developing countries. To illustrate, around 60 percent of the total health expenditure in sub-Saharan Africa in 2005 was financed by private sources, mostly through out-of-pocket payments. Expenditures on private providers accounted for half of this total expenditure (International Finance Corporation, 2007). In many contexts the private sector also employs a sizeable proportion of the human resources needed to deliver health services—a recent assessment in Kenya found that more than 60 percent of health providers in that country work in the private health sector (Barnes et al, 2009).