Bioenergetic electron transfer chains contain both 1-electron (hemes etc.) and 2-electron (NAD(P), quinones, flavins etc.) compounds. The latter undergo either two consecutive one-by-one (non-cooperative) or simultaneous (cooperative) 2-electron redox reactions. The interfacing of 2- and 1-electron steps is crucial for key phenomena in bioenergetics such as for example electron bifurcation. First observed in mitochondrial Complex III, electron bifurcation has recently been recognised as fundamental to bioenergetics following the discovery of the flavin-based process by the Buckel and Thauer groups. I will argue that electron bifurcation arises from cooperative 2-electron electrochemistry, try to provide an intuitive understanding of the underlying principles and compare the systems studied to date.