  In this article we review recent theoretical and experimental developments on
multilongitudinal-mode emission in ring cavity lasers, paying special attention
to class B lasers. We consider both homogeneously and inhomogeneously broadened
amplifying media as well as the limits of small and large cavity losses (i.e.,
we treat cases within and outside the uniform field limit approximation). In
particular we discuss up to what extent the experimental observations of
self-mode locking in erbium-doped fiber lasers carried out in recent years are
a manifestation of the Risken-Nummedal-Graham-Haken instability.
