Abstract: Conventional electronics completely ignores the electron spin, which provides us with an unprecedented chance and new starting point to explore the future of the modern semiconductor and information industry. Spintronics, or spin-based electronics, aims to exploit the subtle and mind-bending esoteric quantum properties of the electron to develop a new generation of electronic devices. In this paper the motivation, fundamental physics, and scope of spintronics will be briefly addressed. The spin current, one of the essential concepts in spintronics, will be discussed in detail, introducing its definition, physical effects, and recent theoretical and experimental progress.