I review quite briefly for reasons of lengtli, tlie reaction '^C(a,)^"'0 tliat follows core hydrogen burning and governs, with the triple-a process, most of the universal abundances of '^C and "O, including new and previously unpublished work. The present status of the '^C(a,7) "O cross section knowledge and its consequences on the reaction rate uncertainties are presented with some perspective to reach the desired precision at stellar temperatures.