Muon plays an increasingly important role in particle, nuclear, and atomic physics, and in applied research. The muon with the muon neutrino and strange and charm quarks create second generation of the Standard Model particles. Unique properties of muons, including its electric charge, mass, and lack of interaction via strong force made this particle a unique tool for discoveries of new elementary particles, including the Higgs boson, over last half a century. The prompt (by cascade transitions) and delayed (by weak muon capture) fission of heavy nuclei in muonic atoms became an important...