  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.
