Diamond chemical vapour deposition (CVD) thought of as a crystal growth process, is a thermodynamic paradox because it violates fundamental principles of thermodynamics. The most astonishing violation is the experimental observation that CVD diamond can form in gaseous environments that are carbon under-saturated with respect to diamond. A new concept of CVD diamond formation that describes the process in terms of thermodynamics, without any violation of the latter, is presented. According to the present concept the diamond formation is a chemical process consisting in accretion of polymantane macromolecules. The process proceeds on surfaces of polymantane seed macromolecules which are identical to diamond crystals which have H-terminated surfaces. Chemical thermodynamics insist that the Gibb＇s energy of reaction describing the process, Delta G, has a large negative value for the process to be able to proceed. However, under certain conditions, the diamond CVD may not proceed even if Delta G much less than 0, because the process may be kinetically hindered. Such a situation occurs at "low" temperatures at which the abstraction of hydrogen atoms from H-terminated diamond seed crystal surfaces by free hydrogen atom impact followed by the addition of new carbon atoms to the diamond lattice, is a rate-limiting step. The kinetic parameter determining the rate of this step is correlated with thermodynamic instability, Tl, of H-terminated diamond seed crystal surfaces. Using Delta Gand T/functions, one can derive correlations between the film-phase composition as well as the growth-rate and process variables. The dependencies predicted by the present model are in excellent agreement with reported experimental data.