Spintronics is a new branch of electronics in which electron spin in addition to its charge is manipulated to yield a desired outcome. Spintronic devices act following a simple scheme: Information is stored (written) into spins as a particular spin orientation; Spins, attached to mobile electrons, carry the information; Information is read at a terminal. Spin orientation of conduction electrons survives for a relatively long time, which makes spintronic devices particularly attractive for memory storage and magnetic sensors applications and potentially for quantum computing where electron spin would represent a bit (called qubit) of information. In this book, we have discussed four spintronics phenomena, such as GMR, TMR, spin-transfer torque mechanism and magnetic domain wall motion memory. We have also discussed applications, such as GMR magnetic read head and MRAM employing TMR. Many spintronic devices are in progress. Those are expected to be non-volatile, versatile, fast, capable of simultaneous data storage and processing and consuming less energy. Spintronics revolutionizes high-density data storage, microelectronics, sensors, quantum computing, biomedical applications etc.