AbstractMitochondria can form ATP from ADP and inorganic phosphate, the required energy being supplied by respiration. This coupled process, which in sufficiently aerated normal animal cells furnishes the bulk of the cellular ATP, is termed oxidative phosphorylation. The overall reaction is intimately associated with the mitochondrial inner membrane and proceeds via a primary high‐energy intermediate. This intermediate, in a manner as yet unknown, energizes the anhydride formation between ADP and inorganic phosphate. The coupling between respiration and ATP synthesis is mediated by proteins of the mitochondrial inner membrane which are known as “coupling factors”. The mechanism of oxidative phosphorylation is at present being discussed in terms of three hypotheses which are generally referred to as “chemical”, “chemiosmotic”, and “conformational” hypotheses. None of these hypotheses has as yet been experimentally verified.