  The synchrotron-emitting nebulae formed by energetic winds from young pulsars
provide information on a wide range phenomena that contribute to their
structure. High resolution X-ray observations reveal jets and toroidal
structures in many systems, along with knot-like structures whose emission is
observed to be time-variable. Large-scale filaments seen in optical and radio
images mark instability regions where the expanding nebulae interact with the
surrounding ejecta, and spectral studies reveal the presence of these ejecta in
the form of thermal X-ray emission. Infrared studies probe the frequency region
where evolutionary and magnetic field effects conspire to change the broadband
synchrotron spectrum dramatically, and studies of the innermost regions of the
nebulae provide constraints on the spectra of particles entering the nebula. At
the highest energies, TeV gamma-ray observations provide a probe of the
spectral region that, for low magnetic fields, corresponds to particles with
energies just below the X-ray-emitting regime.
  Here I summarize the structure of pulsar wind nebulae and review several new
observations that have helped drive a recent resurgence in theoretical modeling
of these systems.
