Effective health care interventions are underutilized in the developing world, and income-related disparities in use are large. The evidence concerning this access problem is summarized and its demand side causes are identified. Broad strategies that have been proposed to tackle the access problem through changes in economic incentives are considered. It is argued that there is a need to go beyond the identification of broad strategies to the design and evaluation of specific policy measures. Only through experimentation and evaluation will we learn what works in raising health care utilization, particularly among the poor in the developing world