  The large-scale structure of pulsar wind nebulae (PWNe) tells us a
considerable amount about their average magnetic fields, the total particle
input from the pulsar winds, and the confining pressure at their outer
boundaries. However, the details of the pulsar outflow, the sites of shocks and
particle acceleration, the effects of instabilities in the magnetic field, and
the interaction between the relativistic wind and the surrounding ejecta are
contained in small-scale structures, where we observe jets and toroidal
structures, time-varying emission from compact clumps, and filaments in both
the inner and outer regions of the nebulae. Here I review recent observational
studies of compact structures in PWNe and present current scenarios (and
questions) regarding their origin.
