Estimates vary, but it is thought that wave and tidal power could provide 15-20% of the UK's energy requirements. However, at present the field is immature, with the first device connected to the grid this July (2008). Furthermore, the field is complex, with at least 50 different technologies to extract energy from the oceans at various stages of development. Many of these technologies have undergone testing at the European Marine Energy Centre (EMEC) in Shetland and other sites around the UK. This POSTnote aims to investigate the range of technologies available, focusing on those nearing the commercial development stage. Issues surrounding marine technology such as energy transport, variability of power supply and the harsh conditions of the ocean environment will be investigated and the relative merits of wave and tidal power considered. The note will also consider the role that marine renewables could play in meeting the EU mandated target to produce 15% of the UK's energy from renewable sources by 2020.