This second, revised and thoroughly updated edition of the successful textbook by Claus Grupen describes the branch of astrophysics known as astroparticle physics. Using experimental methods known from cosmic ray and particle physics, astroparticle physics investigates processes of highest energies taking place in the universe. The new edition reports on progress made by recent discoveries in gravitational wave astronomy and neutrino astronomy (including all details needed to understand recent discoveries in multi-messenger experiments) and also astrobiology. After a historical introduction to the basics of elementary particles the author describes their interactions and the relevant detection techniques. The main body of the book concerns cosmic rays as well as particle processes in astrophysics and cosmology including the physics of the early universe. The book provides an orientation in the field of astroparticle physics that many beginners might be looking for. It also presents new sections exploring the interface between particle physics and cosmic radiation and illustrates the impact of particle physics discoveries to astroparticle physics. The physics is presented using little mathematics, and the results are illustrated by many diagrams and illustrative scientific cartoons which ease the reading of the book. Closing the gap between expert and popular level, the book is highly recommended for undergraduate students in physics or astronomy. It also includes an extensive glossary and a detailed index.