Some redox chemistry and biochemistry of p-benzoquinones are summarised. In particular, the behaviour of quinols and quinones at electrode surfaces and in solution, together with the mechanism of reduction of soluble cytochrome c by quinols, produces a model of electron transfer relevant to biological systems. In such a model the biological transfers occur by collisional reactions of the quinone and quinol with the protein donors and acceptors. After collision, the detailed reactions occur via bound enzyme intermediates but electronic mobility between the donors and acceptors is provided by diffusional mobility of the quinone molecules. Such considerations have allowed a detailed investigation of the redox reactions of quinols with a complex biological multiprotein system, the bc complex. A probable mechanism of electron transfer into and through this complex is presented, together with some discussion of the mechanism of energy transduction which would operate in the intact biological system.