Muon plays an important role in elementary particle, nuclear and atomic physics. Muon was discovered in 1936 in cosmic radiation. At present, it is very important in the framework of the Standard Model. With the discovery of a charm quantum number, muon and the accompanying muon neutrino play an important role in the quark-lepton model of elementary particles being combined in the second generation of the Standard Model. Muonic processes provide important information on the low energy limit of the weak interaction. This book describes the various aspects of muon physics, taking into account the most recent experiments conducted.