Galaxy clusters are the largest gravitationally bound objects in our Universe and they are unique laboratories to study fundamental questions in astrophysics. In a growing number of clusters diffuse extended radio emission has been found.  The existence of this diffuse radio emission implies the presence of extremely energetic cosmic rays in the intracluster medium. Since these diffuse cluster radio sources have steep synchrotron spectra they are best studied at low radio frequencies. In this talk I will discuss how galaxy clusters can act as giant particle accelerators, producing these energetic cosmic rays.