  In the last few years, new observations by CHANDRA and XMM have shown that
Pulsar Wind Nebulae present a complex but similar inner feature, with the
presence of axisymmetric rings and jets, which is generally referred as {\it
jet-torus structure}. Due to the rapid growth in accuracy and robustness of
numerical schemes for relativistic fluid-dynamics, it is now possible to model
the flow and magnetic structure of the relativistic plasma responsible for the
emission. Recent results have clarified how the jet and rings are formed,
suggesting that the morphology is strongly related to the wind properties, so
that, in principle, it is possible to infer the conditions in the unshocked
wind from the nebular emission. I will review here the current status in the
modeling of Pulsar Wind Nebulae, and, in particular, how numerical simulations
have increased our understanding of the flow structure, observed emission,
polarization and spectral properties. I will also point to possible future
developments of the present models.
