  Pulsar glitches are thought to be probes of the superfluid interior of
neutron stars. These sudden jumps in frequency observed in many pulsars are
generally assumed to be the macroscopic manifestation of superfluid vortex
motion on a microscopic scale. Resolving and modelling such phenomena on the
scale of a neutron star is, however, a challenging problem which still remains
open, fifty years after the discovery of pulsars. In this article I will review
recent theoretical progress, both on the microscopic level and on the
macroscopic level, and discuss which constraints on the models can be provided
by observations.
