What explains sub-national variation in the quantity and quality of public welfare services provided in poor developing countries? The literature on this question is suggestive at best. Explanations for differences in financial, human, and infrastructural resource allocations and the effectiveness with which they are used suggest the importance of, respectively, competition for electoral support, clientelist politics, and, to a lesser extent, donor preferences. This paper will test these competing theories by examining the spatial variation in allocations for and quality of state health services provided in Yemen, a low-income developing country with competitive local elections, powerful tribal and patronage networks, and substantial international donor investments. It exploits new geo-referenced data on the locations and funding of government health service providers in all 333 of Yemen’s districts since 1994 to the present, in addition to data on district-level electoral outcomes, tribal affiliations of local politicians, and international aid transfers for the same period; surveys on the quality of health services; and interviews with major donor agencies on aid strategies and priorities in the health sector. The study will provide a better understanding of the uneven patterns of public access to state-provided social services in a developing country context, and the relative importance of political competition, patronage, and donor factors influencing these patterns at the local level.