This article examines the economics of groundwater irrigation and shallow tubewell (STW) ownership decision making, using farm-level data collected from 324 households in Nepal. STW irrigation generated a significant positive effect on rice yield and farmers' incomes. Based on a probit model, the farm size, land fragmentation, access to electricity, and access to credit were found to significantly influence farmers' decisions to own STWs. Although the water market benefited poor farmers, it is too small and monopolistic. Policy reforms needed to make groundwater accessible to the poor majority include effective credit programs, investments in rural electrification, and public sector support for promoting suitable pumping technologies.