This book provides a comprehensive description of the volcanological, petrological and geochemical features of the Poás Volcano (Costa Rica), one of the most active volcanic systems in Central America and part of the Central America Volcanic Arc (CAVA). Poás Volcano hosts a unique sulfur lake, which actually is one of the world's most acidic lakes, and has experienced molten sulfur eruptions. Past investigations, current monitoring activities and planned programs of investigation into lessening of the volcanic hazard are reported here. Specific sections of the monograph will be devoted to the impact of this volcano on the social, agricultural and industrial activities in the area. Legends and popular traditions related to this volcano will be described in the last chapter to round up a complete scientific review on this unique volcanic system.