  A very important aspect of the radio emission from galaxy clusters is
represented by the diffuse radio sources associated with the intracluster
medium: radio halos and relics. These radio sources indicate the existence of
large scale magnetic fields and of a population of relativistic electrons in
the cluster volume. The observational results provide evidence that these
phenomena are related to cluster merger activity, which supplies the energy to
the reacceleration of the radiating particles. The details of the halo-merger
connection are investigated through the comparison between the radio and the
X-ray emission.
