  I discuss the physics of non-Abelian plasmas which are locally anisotropic in
momentum space. Such momentum-space anisotropies are generated by the rapid
longitudinal expansion of the matter created in the first 1 fm/c of an
ultrarelativistic heavy ion collision. In contrast to locally isotropic plasmas
anisotropic plasmas have a spectrum of soft unstable modes which are
characterized by exponential growth of transverse chromo-magnetic/-electric
fields at short times. This instability is the QCD analogue of the Weibel
instability of QED. Parametrically the chromo-Weibel instability provides the
fastest method for generation of soft background fields and dominates the
short-time dynamics of the system. The existence of the chromo-Weibel
instability has been proven using diagrammatic methods, transport theory, and
numerical solution of classical Yang-Mills fields. I review the results
obtained from each of these methods and discuss the numerical techniques which
are being used to determine the late-time behavior of plasmas subject to a
chromo-Weibel instability.
