The chapter discusses the role of active galactic nuclei (AGN) in heating the hot gas in galaxy clusters. High-resolution X-ray spectroscopy has shown that the hot gas in clusters is not cooling at the predicted rates, and X-ray images reveal giant cavities and shock fronts that provide a direct means of measuring the energy injected into the hot gas by AGN. Radio jet powers are near those required to offset radiative losses and suppress cooling in isolated giant elliptical galaxies and larger systems. This suggests that heating and cooling are coupled by feedback, which suppresses star formation and the growth of luminous galaxies. The conversion of jet energy into heat and the contribution of other heating mechanisms, such as thermal conduction, are not well understood. Outburst energies require substantial late growth of supermassive black holes. If all the required energy is deposited in the cooling regions of clusters, AGN outbursts must alter large-scale properties of the intracluster medium. The chapter also covers the structure of radio lobes and cavities in cluster cores, shock fronts, and the impact of AGN on galaxy formation and feedback mechanisms.The chapter discusses the role of active galactic nuclei (AGN) in heating the hot gas in galaxy clusters. High-resolution X-ray spectroscopy has shown that the hot gas in clusters is not cooling at the predicted rates, and X-ray images reveal giant cavities and shock fronts that provide a direct means of measuring the energy injected into the hot gas by AGN. Radio jet powers are near those required to offset radiative losses and suppress cooling in isolated giant elliptical galaxies and larger systems. This suggests that heating and cooling are coupled by feedback, which suppresses star formation and the growth of luminous galaxies. The conversion of jet energy into heat and the contribution of other heating mechanisms, such as thermal conduction, are not well understood. Outburst energies require substantial late growth of supermassive black holes. If all the required energy is deposited in the cooling regions of clusters, AGN outbursts must alter large-scale properties of the intracluster medium. The chapter also covers the structure of radio lobes and cavities in cluster cores, shock fronts, and the impact of AGN on galaxy formation and feedback mechanisms.