In this study, detailed information about the fundamentals, energy and power potentials, devices, technologies, installed capacities, annual generation, and future of ocean energy sources: tidal, wave, temperature and salinity gradients are given as an up to date global review. Detailed analysis showed that aggregate global annual potential of different ocean energy sources is significantly greater than our global annual electricity demand. As a result, many countries around the globe aim to utilise ocean energy sources for power generation. However, this is currently not possible on a large scale because most of the ocean energy technologies are still under development and there are many economic, technical and environmental problems to be solved. Therefore, the research and development in ocean energy engineering should be fostered by governments and private sector around the globe so that we can use these reliable and clean renewable energy sources for supplying our increasing global electricity demand. Finally, this study could offer some assistance to the academia and industry for the utilisation of different ocean energy sources for achieving a sustainable future.