  Radio pulsars provide us with some of the most stable clocks in the universe.
Nevertheless several pulsars exhibit sudden spin-up events, known as glitches.
More than forty years after their first discovery, the exact origin of these
phenomena is still open to debate. It is generally thought that they an
observational manifestation of a superfluid component in the stellar interior
and provide an insight into the dynamics of matter at extreme densities. In
recent years there have been several advances on both the theoretical and
observational side, that have provided significant steps forward in our
understanding of neutron star interior dynamics and possible glitch mechanisms.
In this article we review the main glitch models that have been proposed and
discuss our understanding, in the light of current observations.
