Spin-orbit coupling and spin transport

Recent achievements in semiconductor spintronics are discussed. Special attention is paid to spin-orbit interaction, coupling of electron spins to external electric fields, and spin transport in media with spin-orbit coupling, including the mechanisms of spin-Hall effect. Importance of spin-transport parameters at spin-precession wave vector $k_{\rm so}$ is emphasized, and existence of an universal relation between spin currents and spin accumulation at the spatial scale of $\ell_{\rm so}\approx k_{\rm so}^{-1}$ is conjectured.