The high elevation biota of the world have been the subject of many synthetic approaches, including assessments of the variability and diversity of ecosystem properties and processes, ecophysiological traits and organismic functioning in general. This chapter discusses questions relating to high elevation biodiversity. Tropical mountains may span the range from the humid lowland forest to glaciated mountain tops, and it is therefore no surprise that the regions become hot spots of biodiversity. Less steep declines are seen in genera and family numbers in plants, which means that certain families contribute more to high elevation biodiversity than others. The island nature of mountains may even have enhanced biodiversity, certainly the degree of endemism is increased. The atmospheric changes may be much less significant for biodiversity than changes in land use, but all of them are potentially important in affecting species richness.