The various aspects of the chemistry involved in the oxidative coupling of methane are considered, with special focus on the surface chemistry, i.e., on the heterogeneous part of this complex hetero-homogeneous process. The elementary steps which control either the primary or the secondary reactions are analysed in the light of recent results obtained with state-of-the-art techniques such as the isotopic transient kinetics and the fast pulse TAP reactor. The two main routes for methane activation via homolytic or heterolytic splitting of the C-H bond are discussed together with the modes of oxygen activation and their dependence on the catalyst nature. A tentative list of various active sites corresponding to the specific stages of the reaction is provided. In view of a better understanding of the secondary conversion of ethane into ethylene and further on into COx, recent studies devoted to the oxydehydrogenation of ethane are reviewed with an introduction to the development of low temperature processes. The occurrence of a single mechanism or of several ones adapted to the various families of active catalysts is discussed on the basis of the huge amount of literature available at the present time.