Himalayan rivers like Ganges and Indus are the source of fresh water and livelihood for millions living in the mountains and the downstream regions. The Himalayan glaciers and snow together with the base flow from the high mountains contribute important components of flows rendering the rivers perennial in nature. As water resources are inextricably linked with climate and other anthropogenic changes, global change is quite likely to alter significantly the flow patterns of the Himalayan rivers with consequent impacts on the economy in terms of water availability, food security and hydropower generation. Investigations on global change impact assessment on Himalayan hydrology involves the evaluation of changes in the snow and glacier dynamics as well as runoff resulting from changes in climatic, hydrological and local anthropogenic parameters. Such an ongoing investigation carried out in a few selected watersheds in the Himalayan region under a regional collaborative effort is briefly described and some results thus obtained are also presented and discussed.