A CGD Working Paper with George Yang. There is considerable interest in increasing private participation in infrastructure to meet the twin goals of climate mitigation and development in low- and middle-income countries. At the same time, this infrastructure needs to make returns in order to be financially sustainable. This paper reviews evidence on the economics of infrastructure investment and the role of human capital and uses two approaches to provide additional evidence on the link between human capital and infrastructure returns: (i) using estimated returns to individual World Bank infrastructure projects and their relationship to country levels of human capital and (ii) broader approaches linking the macroeconomic impact of infrastructure investment in the presence of varying human capital stocks.