arXiv : 0904 . 1999 v 1 [ cond - mat . mes - hall ] 13 Apr 2009 1

This article discusses spin transport in systems with spin-orbit interactions and how it can be understood in a semiclassical picture. I will first present a semiclassical wave-packet description of spin transport, which explains how the microscopic motion of carriers gives rise to a spin current. Due to spin non-conservation the definition of the spin current has some arbitrariness. In the second part I will briefly review the physics from a density matrix point of view, which makes clear the relationship between spin transport and spin precession and the important role of scattering.