The Hindu Kush-Himalayan (HKH) region is one of the most ecologically sensitive and fragile areas in the world. In all likelihood, the effects of climate change will become evident here first and with the greatest intensity. This report synthesises the present knowledge about the consequences that climate change could have for the region. This thorough review of the existing literature, based on over 360 references, was prepared in consultation with more than 80 leading experts from the region and abroad. To identify and bridge gaps in climate change related knowledge for the HKH, leading experts in climatology, hydrology, environmental science, and other climate-related fields from across and beyond the region gathered at an Authors’ Workshop in Kathmandu on 18 and 19 August 2011. The workshop presentations and discussions form the backbone of this report, fleshed out with additional literature. Rigorous review sought to ensure a thorough and relevant report. The report captures the cutting-edge knowledge from the region in three major areas: climate and hydrology; biodiversity and ecosystems; and atmospheric changes. It also indicates gaps in knowledge and shows a way forward for systematic data acquisition and data sharing in the areas of biophysical observation, socioeconomic analysis, and policy research. This report not only should be of interest to planners and policy makers in the region, but should also provide vital inputs into global climate change negotiations.