Spintronics exploits the electron’s spin degree of freedom to go beyond the capabilities of conventional charge-based electronics. Since the discovery of giant magnetoresistance, the field has evolved from the study of spin-polarized transport in ferromagnets to a broader framework encompassing spin-orbit coupling, collective spin dynamics, and electric-field control of magnetic states. In this Review, we discuss the physical mechanisms that underpin modern applied spintronics, with particular emphasis on spin-charge interconversion, magnetoresistive effects, and the electrical detection and manipulation of collective spin phenomena. We examine how spin currents, spin-orbit torques, and voltage-controlled magnetic properties enable efficient control of magnetization and magnetic excitations in nanoscale devices. These mechanisms form the basis of key technologies such as magnetic sensors and magnetic random-access memory (MRAM) while also opening pathways toward emerging architectures including racetrack memories, spin-based logic, and unconventional computing. By highlighting common principles across materials platforms and device concepts, we provide a perspective on the current state of spintronics and outline promising directions for future spin-based electronics.