  Observations indicate that magnetic fields on neutron stars span at least the
range $10^{8-15}$ G, corresponding to a range of magnetic fluxes similar to
that found in white dwarfs and main sequence stars. The observational evidence
is discussed, as well as the possible origin of the field, and the associated
phenomenology (``classical'', millisecond, and binary pulsars, ``magnetars'',
etc.). Particular attention is given to physical processes potentially leading
to magnetic field evolution.
