expand at sub-sonic speeds (where the internal lobe and ram pressures are comparable to the external pressure), they do $p{\rm d}V$ work on the hot gas. When the lobes expand at supersonic speeds, we expect additional work to be done to shock-heat the gas. This is a non-adiabatic process that effects the entropy as well as the internal energy of the external medium.

However, it is only recently that we have been able to make detailed statements about the internal and external pressures of FRII radio galaxies in typical environments, which determine their dynamics. This change has come about because the current generation of X-ray telescopes, [*XMM-Newton*]{} and [*Chandra*]{}, have the ability to detect inverse-Compton emission from the lobes together with thermal emission from their hot gas environments, which are often relatively poor (@cbhw04; @kbhecwm07; @hec07; @bwhc07). Detection and characterization of these X-ray components allows us to describe the current dynamics of the radio lobes and gives us some idea what the energy input to the external environment over the lifetime of the radio source must have been. The impact that the AGN outbursts have on the hot IGM has implications for the history and evolution of the hot phase 