  Pulsars, or more generally rotation powered neutron stars, are excellent
factories of antimatter in the Galaxy, in the form of pairs of electrons and
positrons. Electrons are initially extracted from the surface of the star by
the intense rotation induced electric fields and later transformed into
electron-positron pairs through electromagnetic cascading. Observations of
Pulsar Wind Nebulae (PWNe) show that cascades in the pulsar magnetosphere must
ensure pair multiplicities of order $10^{4}-10^{5}$. These pairs finally end up
as part of the relativistic magnetized wind emanating from the pulsar. The wind
is slowed down, from its highly relativistic bulk motion, at a termination
shock, which represents the reverse shock due to its interaction with the
surrounding ejecta of the progenitor supernova. At the (relativistic)
termination shock, acceleration of the pairs occurs, as part of the dissipation
process, so that the cold wind is transformed into a plasma of relativistic
non-thermal particles, plus a potential thermal component, which however has
never been observed. As long as the pulsar wind is embedded in the supernova
remnant these pairs are forced to escavate a bubble and lose energy
adiabatically (because of the expansion) and radiatively (because of magnetic
and radiation fields). We discuss here the observational constraints on the
energy and number content of such pairs and discuss the scenarios that may
allow for the pairs to escape in the interstellar medium and possibly
contribute to the positron excess that has recently been detected by the PAMELA
satellite. Special attention is dedicated to the case of Pulsar Bow Shock
Nebulae. The pairs produced in these objects may be effectively carried out of
the Supernova Remnant and released in the Interstellar Medium. As a result, Bow
Shock Pulsar Wind Nebulae might be the main contributors to the positron excess
in the Galaxy.
