The past 30 years has witnessed the elucidation by biochemical and biophysical methods of the detailed structures and mechanisms of the chain of respiratory protein complexes found in the inner membranes of mitochondria and in the cytoplasmic membranes of eubacteria. These efforts have led to a deep understanding of the fundamental processes involved in the energy conversion processes upon which all life depends. In the lecture, this progress will be reviewed and the outstanding residual problems will be discussed. Particular emphasis will be placed on recent progress towards understanding how adenosine triphosphate is made by the human ATP synthase, and on possible emerging roles as a target for combatting infectious diseases.