In recent years the population of the Hindu Kush Himalayas (HKH) has been confronted with rapid social, economic, demographic, and political changes. In addition, the region is particularly vulnerable to climate change. However, there is a scarcity of cohesive information on the state of the environment and on the socioeconomic situation of the approximately 210 million people who reside in the HKH. Specifically, data on livelihood vulnerability and responsive behavior is lacking. To address this gap the International Centre for Integrated Mountain Development (ICIMOD) has developed the Vulnerability and Adaptive Capacity Assessment (VACA), a research tool to explore livelihood vulnerability to environmental and socioeconomic change as well as adaptive capacity in the mountain context. As part of the Himalayan Climate Change Adaptation Programme (HICAP), ICIMOD has carried out a representative quantitative survey that interviewed about 6,100 households in three sub-basins in the HKH region: the Upper Indus sub-basin in Pakistan, the Eastern Brahmaputra sub-basin in India, and the Koshi sub-basin in Nepal. The chapter discusses the operationalization of vulnerability in the VACA questionnaires, the research design of the VACA survey, and first findings for the three sub-basins.