There is a general increase in the awareness of political, business and financial institutions for the necessity of concrete action to allow sustainable development in mountain regions. This increased interest in mountain regions is documented by the resolution of the UN General Assembly that declared 2002 the International Year of Mountains. The world’s mountains clearly do not lend themselves to a simple definition because of their complexity. For each region, specific characterisation is necessary. The Arctic and Alpine regions of Europe often represent the most remote and least disturbed natural environments; yet they are threatened by acid deposition, toxic air pollutants and by climate change. These environments are fragile, being subject to adverse and harsh climatic conditions (high levels of precipitation, low temperatures, aridity, high solar radiation), natural disasters (avalanches, earthquakes, volcanic eruptions), and poor, shallow soils prone to erosion because of steep slopes. However, the fragility of mountain ecosystems means that they are not only vulnerable to environmental change, but that they are also excellent sensors of change. Their sensitivity and the presence of high quality environmental records preserved in lake sediments can be used to infer the speed, direction and biological impact of changing air quality and climate.