A review of gas phase and surface kinetics of hydrogen radicals in plasma chemistry is presented. It is shown that the presence of rovibrationally excited hydrogen molecules strongly influences the mechanisms of the chemical reactions. Both homo- and heterogeneous collisional processes are analysed in that respect. As will be shown, ionizing plasmas are dominated by gas phase rovibrational excitation phenomena. By contrast the kinetics of recombining plasmas are strongly influenced by heterogeneous elementary processes, where they can be distinguished in a natural way. Examples of heterogeneous catalysis in plasmas, i.e. particle excitation phenomena at surfaces, are discussed.