Growing films on metals are compared with current‐producing cells under more general conditions. The assumptions made in connection with the development of the laws are discussed. When the electrical resistances are small, the growth rate may be controlled by some mechanical limitation. Since the linear law for such a condition is obeyed only when the controlling factor imposes a constant growth rate, it is likely that this law is more the exception than the rule. The parabolic law is obeyed if the electrical resistances control the growth rate and it is expressed by the general equation when any constant resistances, such as that which may be required to transfer the electrons and cations across the metal‐film interface, are added to the electronic and electrolytic resistances of the films. In a film that is completely polarized, the concentration gradient diffusion of the cations and anions determines the transfer of the electrons across the film and the parabolic law breaks down. It is shown that contradictions are involved in the assumptions usually made in deriving the parabolic growth law, and that from a theoretical point of view the actual growth curve may depart widely from a parabolic curve. The growth curve would seem to fall below the curve which would be expected if the parabolic law should be obeyed, but it cannot be predicted that it would be logarithmic. A statement is made concerning the mathematical problem which must be solved in order to have a sound theoretical basis for the derivation of laws governing the growth of oxide and tarnish films when the ions migrate by diffusion processes.