Whilst wind power is currently the main form of renewable energy generation in the marine environment, developments in the fields of wave and tidal power in recent years have brought these technologies to the forefront of renewable energy generation. Wave and tidal energy conversion devices have been in development for many years and numerous pilot projects for these devices are now underway in many countries across Europe, as well as areas such as Canada and the United States. In Europe, most developments of marine renewable energy installations (MREIs) require an Environmental Impact Assessment, the purpose of which is to ascertain the effects of the development on the natural environment, species, biological and physical processes. The permitting process can then weigh the scale of such impacts on the environment against the value of the installation in order to determine whether consent to proceed with the development will be granted or not. While some of the effects of introducing MREIs to the marine environment will be the same regardless of the installation involved, other effects will be device-specific. Effects will vary with the stage (construction, operation and decommissioning) and scale of the project, and will depend on location and the ecosystem in that area.