Enzymatic bioelectrocatalysis involves the application of enzymes to facilitate the conversion of chemical to electrical energy. This approach has been widely applied in the fields of biosensing, biofuel cells, and to a lesser degree the synthesis of fine chemicals. While direct electrochemical communication between the enzymes and electrodes is generally preferable, it is often the case that efficient electron transfer rates can only be achieved when redox mediators are employed to shuttle electrons reversibly from the redox site of the enzyme to the electrode interface. Unfortunately, there still exist many oxidoreductases for which no effective exogenous mediator is known. This may be due to insufficient understanding of the role that molecular structure of the mediator plays in determining its ability to facilitate electron transfer to a given enzyme. Consequently, selection and/or design of novel redox mediators remains a challenge that is often accomplished using a “guess and check” approach to maximize electron transfer rates. Developing a rapid, and convenient method of predicting the role played by other structural and chemical features beyond redox potential of a mediator is an important goal in advancing mediated bioelectrocatalysis. This talk will describe our recent efforts in identifying structure - function relationships of redox mediators that control efficient electron transfer rates. I will highlight results from stopped-flow spectrophotometry experiments which review the nature of electron transfer events between quinone redox couples in altering bioelectrocatalytic activity.