The oceans of the earth offer vast amounts of renewable energy. Technologies to harness the power of the seas are at an early stage of development. Even the most advances technologies, namely tidal current and ocean wave still face considerable barriers and many obstacles remain. Research, development and innovation can help overcome those barriers. This review provides an overview over the current state of research in the field of ocean energy. In particular, the authors focus on research beyond technology or technological improvements. This article also highlights areas where research gaps exists and where future research efforts should be directed to.