The hydrological roles of glaciers and seasonal snow in the Indus, Ganges, Brahmaputra, Amu Darya, Syr Darya and Mekong basins are, for the first time, assessed comprehensively at a major river basin scale in this paper. Contribution of glacier runoff, subdivided into renewable and nonrenewable components, and seasonal snowmelt to mean annual flow is evaluated for two time slices: 1961-1990 and 2001-2010. The recent changes of the hydrological roles of glaciers and snow, and the most likely changes of those under future climate change are analyzed.