In the face of climatic and other socioeconomic changes, most South Asian countries having large and growing population, limited land resources, and increasing water stress face a common challenge of how to grow more food with the same or less land, less water, and increased energy prices. This concept paper seeks deeper understanding of the interlinkages among water, energy, and food, which is crucial to formulate cross-sectoral policies for more resilient and adaptable societies. In South Asia, such a nexus approach inevitably needs to take Himalayan ecosystem services into account. Rice and wheat, the staple foods in South Asia, require huge amounts of both water and energy. The Indus-Ganges-Brahmaputra plain - the sub-region's grain basket and one of the world's largest areas of irrigated agriculture - depends in large part on the Himalayan mountain system as a source of both surface and groundwater for irrigation; as a source of hydropower; and as a regulator of climate and a repository of agro-biodiversity.