Chapter ABSTRACT: Mountains make up 24% of the world’s land area, are home to 20% of the world’s population, provide 60–80% of the world’s fresh water, and harbour 50% of the world’s biodiversity hotspots (well-established). The United Nations recognized the importance of mountain ecosystems, both for conserving biological diversity and for sustaining humanity, in Chap. 13of Agenda 21. More generally, ecosystem diversity, species diversity, genetic diversity, and functional diversity all play key roles in the ecosystem services that benefit people and communities (well-established).