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.

In this talk I will summarize the structure of pulsar wind 
nebulae,
emphasizing how new observations have helped drive a 
recent resurgence
in theoretical modeling of these systems.