  Persistent currents in mesoscopic normal metal rings represent, even a decade
after their first experimental observation, a challenge to both, theorists and
experimentalists. After giving a brief review of the existing -- experimental
and theoretical -- results, we concentrate on the (proposed) relationship of
the size of the persistent current to the phase breaking rate. In particular,
we consider effects induced by noise, scattering at two-level systems, and
magnetic impurities.
