Muon Physics, Volume II: Weak Interactions deals with the weak interaction of muon and covers topics ranging from the elementary particle aspects of muon decay and muon capture, as well as the conventional two- and one-neutrino-field theories. The law of lepton conservation is also considered, along with semileptonic weak interactions in nuclei. This volume is comprised of two chapters and begins with a discussion on muon decay and muon capture, offering a theoretical interpretation of the elementary-particle aspects of the decay of a muon and the capture of a muon by a proton. The law of lepton conservation is examined in both conventional two- and one-neutrino-field theories. Semileptonic weak interactions in nuclei are also examined, paying particular attention to neutrino reactions, charged-lepton capture, and β decay. The experimental results on weak interactions (low energies) are reviewed in relation to muon decay, rare and ultrarare muon decays, and muon capture. The final chapter is devoted to the interactions of muon neutrinos and limits the discussion to the high-energy type. This book is written primarily for physicists as well as students and researchers in physics.