A good catalyst for converting water into oxygen is seen as an essential part of any sustainable solar-energy conversion scheme. Some success has been achieved using molecular complexes as catalysts and the key factors influencing their performance are discussed. The necessity of generating a solid-state catalytic system is presented and the first attempts to generate supported molecular water-oxidation catalysts are analyzed. During the past four years we have witnessed a revolution in the field of water-oxidation catalysis, in which well-defined molecules are opening up entirely new possibilities for the design of more rugged and efficient catalysts. This revolution has been stimulated by two factors: the urgent need for clean and renewable fuel and the intrinsic human desire to mimic nature’s reactions, in this case the oxygen-evolving complex (OEC) of the photosystem II (PSII). Herein we give a short general overview of the established basis for the oxidation of water to dioxygen as well as presenting the new developments in the field. Furthermore, we describe the new avenues these developments are opening up with regard to catalyst design and performance, together with the new questions they pose, especially from a mechanistic perspective. Finally the challenges the field is facing are also discussed.