**Abstract**

This chapter discusses how to apply the most significant aspects and concepts of modern volcanology to the study the ancient volcanic terrains, where volcanic successions appear exposed in discontinuous outcrops, with various degrees of deformation, which are often manifested in the presence of metamorphosed and hydrothermally altered volcanic rock assemblages. The way to understand paleovolcanism is through the identification and interpretation of the products of past volcanic activity in terms that is equivalent to what is done in modern terrains, despite the difficulty of having to characterize and recompose all those subsequent geological processes that have been superimposed upon them. This chapter summarizes the most fundamental aspects of the study of ancient volcanic terrains, paying special attention to the definition of facies associations, the characterization of their spatial and genetic relationships, and their paleoenvironmental and paleogeographic significance, as well as to the possible causes of the original facies modification. The implications for the presence of volcanism in the dynamics of sedimentary basins and its relationship with different geodynamic environments are also analyzed.

**Keywords:** volcanic processes, volcano-stratigraphy, volcano-tectonics, volcanogenic sediments, alteration processes, paleoenvironmental reconstruction
