  After discussion of observational constraints on the nature of the MHD wind
coupling between the Crab Pulsar and the Crab Nebula, the theory of transverse
relativistic shock structure is reviewed and applied to the interpretation of
the wisps in the Nebula as the manifestation of the distributed wind
termination shock structure, energetically dominated by heavy ions, accelerated
in the rotational equator of the pulsar to energies comparable to the total
voltage across the pulsar's open field lines and carrying a current comparable
to the Goldreich- Julian current. New results on the variability of the shock
structure are presented, which show that the gyrating ion bunches emit
outwardly traveling finite amplitude compressional waves, in agreement with
recent ground based observations. The implications of the theory for X-ray,
$\gamma$-ray and high energy neutrino emission are briefly discussed, as are
the problems of low magnetic energy density in the upstream wind and the origin
of the Nebular radio emission. A brief discussion of other plerions leads to
the conclusion that much more detailed observations are needed before these
systems can be modeled with the same sophistication as can be done for the Crab
Nebula.
