  The extended nebulae formed as pulsar winds expand into their surroundings
provide information about the composition of the winds, the injection history
from the host pulsar, and the material into which the nebulae are expanding.
Observations from across the electromagnetic spectrum provide constraints on
the evolution of the nebulae, the density and composition of the surrounding
ejecta, the geometry of the systems, the formation of jets, and the maximum
energy of the particles in the nebulae. Here I provide a broad overview of the
structure of pulsar wind nebulae, with specific examples that demonstrate our
ability to constrain the above parameters. The association of pulsar wind
nebulae with extended sources of very high energy gamma-ray emission are
investigated, along with constraints on the nature of such high energy
emission.
