The features and mechanism of Colossal Magnetoresistance, or CMR, in manganese oxides as well as device physics are highlighted in this book, with a focus on tunneling MR for some artificial structures. Underlying new science, such as tunable electron-lattice interaction in a metal and roles of orbital degrees of freedom in producing an unconventional metallic feature, is also discussed. The book provides a systematic exploration of the CMR materials and an extensive investigation of the electronic phenomena of those compounds by various experimental means.