  Pulsar Wind Nebulae (PWNe) shine at multi-wavelengths and are expected to
constitute the largest class of gamma-ray sources in our Galaxy. They are known
to be very efficient particle accelerators: the Crab nebula, the PWNe class
prototype, is the unique firmly identified leptonic PeVatron of the Galaxy to
date, and most of the PeVatrons recently detected by LHAASO appear to be
compatible with a pulsar origin. PWNe have been proved to be associated with
the formation of misaligned X-ray tails and TeV halos, as sign of an efficient
escape of energetic particles from the PWN into the surrounding medium. With
the advent of the Cherenkov Telescope Array we expect that ~200 new PWNe will
be detected. Being able to correctly model their multi-wavelength spectral
properties, spatial and spectral morphology at gamma-rays is then topical
today. This in particular means we should be able to account for their
different evolutionary phases, and to correctly determine the influence they
have on the spectral properties of the source. This indeed reflects directly on
the expectation of how many PWNe will be detected at gamma-rays. Finally, the
identification of PWNe in future gamma-ray data, not only is relevant for their
scientific importance, but also to allow for the identification of less
prominent sources that might be hidden by the background of non-identified
PWNe.
