This reference work presents, for the first time, the most comprehensive data on the chemical composition of Quaternary andesites from Kamchatka. In addition to detailed chemical analyses, it includes mineralogical phase data, geochemical profiles, rare earth element (REE) concentrations, and isotopic analyses of strontium, neodymium, and oxygen. Essentially, the book aims to create an extensive petrogeochemical database of Kamchatka’s Quaternary andesites. The core of the study—about 65%—consists of data personally collected by the author between 1970 and 2005 during field investigations of Kamchatka’s volcanic eruptions, complemented by detailed petrographic, petrophysical, and geochemical research of Quaternary volcanic rocks. All factual information is organized into tables and diagrams, incorporating literature data with brief references. A key feature of these analyses is their stratigraphic context and precise geological attribution, enabling a clear understanding of the sequence of geological events. The reference explores the petrogenetic characteristics of tholeiitic (mantle-derived, Type I) and calc-alkaline (mantle- and crust-derived, Type II) andesites. It emphasizes the importance of petrophysical, petrographic, and isotopic-geochemical indicators for distinguishing between these two types. Based on the petrophysical database, the book identifies stable, unstable, and intermediate trends in volcanic differentiation. These trends are proposed as tools for interpreting volcanic activity and classifying eruption types. This publication serves as a valuable reference for volcanologists, petrologists, geochemists, and geologists interested in the origins and evolution of volcanic rocks, particularly in the context of Kamchatka’s volcanic activity.