The book at hand documents high mountain biodiversity using the sparsely populated Great Basin region in the southwestern United States as a field laboratory. Its numerous small mountain ranges are separated by low-lying arid valleys. The repeated contrast between alpine and desert environments across one quarter of the North American continent gives rise to a surprisingly rich flora. These alternating basins and mountain ranges are a perfect match to explain patterns and processes in plant diversity using a multi-scale approach. Through this unique methodological concept, the nearly natural and relatively stable ecosystems of the Great Basin Ranges are introduced and important triggers of plant diversity are discussed and evaluated on four different observational scales from micro to macro. Fundamental ecological principles of the Great Basin region are clearly explained and set the stage for conservation of its rich biotic resources. High mountains of the world possess an outstanding biodiversity as compared to their surrounding lowlands and are indeed “hotspots” of plant diversity as clearly presented here. Just as mountains physical properties are manifold, so are the reasons for mountains being biodiversity hotspots: The complex patterns and processes of plant diversity vary with the scale of observation, just as the driving mechanisms may gain or lose or importance with those same changes in scale. The text explains how the multitude of abiotic and biotic environmental factors coexist and change along an altitudinal and latitudinal gradient as they are accompanied by different disturbance regimes and other dynamic processes in an exceptional setting, the American Southwest.