The glacierGlaciers- and snow-fed river basins of the Hindu Kush Himalaya (HKH)Hindu Kush Himalayas (HKH) mountains provide water to 1.9 billion people in Asia. The signs of climate changeClimatechange in the HKHHindu Kush Himalayas (HKH) mountains are clear, with increased warming and accelerated melting of snow and glaciersGlaciers. This threatens the water, food, energy and livelihood security for many in Asia. The links between mountains and plains and the differential impacts of climate changeClimatechange on societies upstream and downstream need to be better established to improve adaptation measures. This chapter sheds light on climate changeClimatechange impacts on the cryosphere and mountains, the impact on river systems and the social consequences of such changes in mountains, hills and plains. In high mountains and hills, the impact of climate changeClimatechange is clear, as seen in changes in agropastoral systems and the increasing occurrence of floodsFloods and droughtsDrought, with losses and damages already high. Moving downstream, the climate changeClimatechange signal is harder to separate from other environmental and management factors. This chapter outlines how climate changeClimatechange in the mountains will impact various sectors in the hills and plains, such as hydropower, irrigationIrrigation, cities, industries and the environment. It discusses how climate changeClimatechange will potentially lead to increased disasters and out-migrationMigration of people. The chapter concludes by highlighting necessary actions, such as the need to reduce emissions globally, build regional cooperation between HKHHindu Kush Himalayas (HKH) countries, increase technical and financial support for adaptation, and more robust and interdisciplinary science to address changing policy needs.