The Altiplano-Puna is a distinctive plateau and pristine environment to study geochemical, ecological, and cli-matic phenomena. It is the second highest plateau on Earth after Tibet and contains the largest endorheic system of South America. Nevertheless, water is a vital resource in the region, and surface water and groundwater are essential sources of drinking water for inhabitants. Environmental characterizations in the Altiplano-Puna plateau are fairly new and increasingly important due to climate change, the sustained decrease of surface water bodies (e.g. Lake Poop ' o), as well as anthropogenic and natural contaminants (e.g. arsenic) which can pollute the scarce water resources. Despite extreme and unique climatic, hydrologic, and geochemical conditions of the Altiplano-Puna plateau, some indigenous populations and biota have adapted. This Special Issue presents seven original research papers covering a wide range of topics in the Altiplano-Puna related to hydrogeochemical, climatic, and anthropogenic processes on the origin and mobility of economically important elements and contaminants, as well as environmental issues and bioindicators of ecological conditions in surface waters. Its aim is to present new and comprehensive analyses with interpretations in this extreme, yet pristine area which has been scarcely characterized from an environmental perspective, and also inspire future studies in the region.