This Viewpoint highlights recent advances in oxygen evolution reaction (OER) catalysis using well-defined/characterized systems and outlines a path for possible further improvements. First, we review our results on ultra-thin film catalysts and compare them to other systems, emphasizing methods that provide accurate intrinsic catalyst activities. We then discuss reports that catalysts with the highest OER activities (in base) often undergo structural and chemical changes during the OER. These findings have implications on how OER catalysts are studied and designed. We suggest opportunities to control molecular-scale interactions in hydrous layered hydroxide/oxyhydroxide catalysts as well as the control of three-dimensional nano- and microstructures using templating approaches.