We propose that an enzyme-catalyzed reaction is best described by a large, three-dimensional potential energy surface, defined by the number of enzyme conformers in one dimension, the number of reaction steps as the second and Gibbs free energy as the third. Aside from accommodating experimental observations that do not fit current mechanistic paradigms, such a surface enables multiple intersecting reaction pathways, pathway funneling, ligand binding energy transduction and kinetic coupling between alternative reaction pathways. The landscape also confers flexibility, enabling an enzyme to seek out an optimal pathway for any reaction conditions that might occur. Thus, coupled pathways enable relatively minor differences in experimental conditions to result in abrupt phenomenological changes in the observed behavior of the reaction.