Book excerpt: This volume presents the possibility of high intensity muon sources whose intensity would be at least 104 higher than that available now. Scientific opportunities anticipated with such sources are search for muon lepton flavor violation, measurements of the muon anomalous magnetic moment and the electric dipole moment, neutrino factories based on a muon storage ring, muon collider and muon applied science such as muon catalyzed fusion and biology. In addition to physics opportunities, the necessary technology for such sources is discussed.