Mountain areas cover almost one quarter of the earth's land surface, with a quarter of the global population living on them or very close by, and they are sources of water, food, timber, minerals and other natural resources. They provide many opportunities for recreation, as well as being centres of biological and cultural diversity and religious significance. Unfortunately, mountain environments and populations are also particularly threatened by climate change and political conflicts, and their inhabitants include many of the poorest and most vulnerable in the world. This publication includes a number of papers which explore a range of sustainable development challenges for mountain regions.