The early history of particle physics cannot be distinguished from the history of cosmic rays. With the advent of accelerators, however, cosmic rays lost their importance in particle physics. This situation persisted until the 1990s, when novel techniques allowed breakthrough discoveries, and exploration of new physics scales now requires going back to cosmic rays. The new profile of scientists in fundamental physics ideally involves the merging of knowledge in astroparticle and particle physics, but the duration of modern experiments is such that people cannot simultaneously be practitioners in both. This book, written by researchers who had been professionals in accelerator physics before becoming leaders of groups in astroparticle physics, bridges the gap; it can be used as a self-training book, a consultation book, or a textbook for a modern approach to particles and fundamental interactions.