  An important area of study of cosmic magnetic fields is on the largest
scales, those of clusters of galaxies. In the last decade it has become clear
that the intra-cluster medium (ICM) in clusters of galaxies is magnetized and
that magnetic fields play a critical role in the cluster formation and
evolution. The observational evidence for the existence of cluster magnetic
fields is obtained by the diffuse cluster-wide synchrotron radio emission and
from rotation measure (RM) studies of extragalactic radio sources located
within or behind the clusters. A significant breakthrough in the knowledge of
the cluster magnetic fields will be reached through the SKA, owing to its
capabilities, in particular the deep sensitivity and the polarization purity.
