Mountain ecosystems belong to the most endangered ecosystems in the world. Especially, the treeline ecotone acts as an indicator for environmental change. However, ecological processes in the treeline ecotone are not yet completely understood. The studies provided in this book may contribute to a better understanding of the interactions between vegetation, climate, fauna, and soils in the treeline ecotone. An introductory chapter is given on plants living under extreme conditions, climate change aspects, and methods for characterization of alpine soils. The following articles focus on mountainous areas in America, Europe and Asia. The Working Group on Mountain and Northern Ecosystems at the Insti- te of Landscape Ecology, University of Münster (Germany), has been working on topics related to the treeline ecotone for several decades. This period under the chairmanship of Friedrich-Karl Holtmeier has come to an end now when he retired in 2004. He initiated numerous studies in high mountains and in the North. Many of his students, who became infected by the ‘mountain virus’, will continue these investigations on ecological processes in the altitudinal and northern treeline ecotones. With this compilation of studies in mountain ecosystems we want to thank Friedrich-Karl Holtmeier for his excellent guidance in these cold and fascinating environments.