Galactic pulsars have been discovered by their radio emission. The emission has the common feature of being periodic, polarized, weakly frequency dependent (in the frequency range 100 MHz 10 GHz). Their energy is large for radio emission but still negligible as compared with the observed emission in the γ-ray range. They are also characterized by a very high temperature of brightness (1027–1031 Kelvin) which implies a coherent emission mechanism (this temperature is much larger than the possible particle energy). The only radiation mechanism which may produce such emission seems to be some kind of relativistic plasma instability. Unfortunately, available plasma models for pulsar magnetospheres are up to now too preliminary to make any definite statement. Nevertheless we will adopt the most popular scenario which relates the radio emission to the field aligned currents (relativistic electrons, positrons, ions) produced in the vicinity of the neutron star. These currents may result from a spark gap mechanism with pair creation (as proposed by Ruderman and Sutherland (1975) and others) or implied by the star's neutrality (as a return current system).