Abstract There are over 200 Pleistocene and Holocene Andean arc volcanoes along western South America, occurring in four distinct segments ( Fig. 5.1 ) called the Northern (NVZ; 2°N–5°S), Central (CVZ; 14°S–28°S), Southern (SVZ; 33°S–46°S) and Austral (AVZ; 49°S–55°S) volcanic zones. In the Andes of Chile alone there are more than 100 Pleistocene and Holocene stratovolcanoes, as well as a number of large volcanic fields and giant caldera complexes, of which 60 have documented Holocene eruptive activity ( Simkin & Siebert 1994 ; González-Ferrán 1995 ). These are located in the CVZ of northern Chile, the SVZ of central-south Chile, and the AVZ of southernmost Chile. Pleistocene and Holocene backarc volcanic centres, the westernmost part of the Patagonian plateau basalts, also occur in southern Chile along the border with Argentina. In addition, intraplate oceanic volcanoes form Chilean islands in the Pacific Ocean, submarine volcanism takes place along the Chile Ridge, and slab-window volcanic activity occurs above the region where the Chile Ridge is currently being subducted, both along the west coast of Chile and in the submarine environment near the trench. Pleistocene and Holocene volcanoes of the Chilean Andes provide a natural laboratory for the study of volcanism, magma genesis and volcanic hazards in the context of oceanic– continental plate collision. Andean volcanic activity results from subduction of the Nazca and Antarctic oceanic plates below the continental lithosphere of western South America ( Fig. 5.1 ). Volcanoes in the CVZ of northern Chile and the SVZ of central-south Chile occur where the angle of