The strong altitudinal gradients in mountain regions provide unique and sometimes the best opportunities to detect and analyse global change processes and phenomena. Meteorological, hydrological, cryospheric and ecological conditions change strongly over relatively short distances; thus biodiversity tends to be high, and characteristic sequences of ecosystems and cryospheric systems are found along mountain slopes. The boundaries between these systems experience shifts due to environmental change and thus may be used as indicators of such changes. The higher parts of many mountain ranges are not affected by direct human activities. These areas include many national parks and other protected environments. They may serve as locations where the environmental impacts of climate change alone, including changes in atmospheric chemistry, can be studied directly. Mountain regions are distributed all over the globe, from the Equator almost to the poles and from oceanic to highly continental climates. This global distribution allows us to perform comparative regional studies and to analyse the regional differentiation of environmental change processes as characterised above. Therefore, within the IGBP an Initiative for Collaborative Research on Global Change and Mountain Regions was developed, which strives to achieve an integrated approach for observing, modelling and investigating global change phenomena and processes in mountain regions, including their impacts on ecosystems and socio-economic systems.