Little is known in detail about the vulnerability of mountain ecosystems in general and the Hindu Kush-Himalayas in particular to climate change, but in these areas of extreme slopes and rapid changes in climatic zones, it is likely that there will be marked impacts on biodiversity, water availability, agriculture, and hazards, and thus on general human wellbeing. Countries face the challenge of developing the detailed scientific knowledge needed to assess the current situation, make projections of likely impacts, and plan for adaptation, but little detailed or long-term research has been carried out in these poorly accessible areas. This publication presents a summary of the findings of an assessment carried out by ICIMOD, together with partners, in the Eastern Himalayas, with support from the MacArthur Foundation. The results of surveys, workshops, stakeholder consultations, and technical papers by individual experts have been synthesised, and used in climate models to develop preliminary climate projections for the region and assess climate change vulnerability. It is hoped that these results will both inform conservation policy at national and regional levels, and stimulate the coordinated research that is urgently needed.