<p>Current research into (photo)electrocatalysis is focused on increasing the reactivity of systems based on Earth-abundant elements, which requires kinetic models of their catalytic mechanisms. In transition metal oxides, adsorption and electron transfer steps typically involve changes in the oxidation state of the metal and the colour of the electrode, which can be measured spectroscopically. In situ spectroelectrochemical studies have exposed the unexpected role played by the density of active species and their co-operativity in dictating (photo)electrochemical performance. Here we review how reaction pathways can be controlled by the presence, or not, of molecular-scale interactions between redox active sites at the interface and discuss strategies to monitor them. We consider how the ability to probe and quantify such interactions opens strategies to enhance catalytic performance and creates opportunities for scientific discovery.</p><p></p>