1. The evidence for anthropogenically induced climate change is overwhelming with the production of greenhouse gases from burning fossil fuels being a key driver. In response, many governments have initiated programs of energy production from renewable sources. 2. The marine environment presents a relatively untapped energy source and offshore installations are likely to produce a significant proportion of future energy production. Wind power is the most advanced, with the development of wave and tidal energy conversion devices expected to increase worldwide in the near future. 3. Concerns over the potential impacts on biodiversity of marine renewable energy installations (MREI) include habitat loss, collision risks, noise, and electromagnetic fields. These factors have been posited as having potentially important negative environmental impacts. 4. Conversely, we suggest that if appropriately managed and designed, MREI may increase local biodiversity and potentially benefit the wider marine environment. Installations have the capacity to act as both artificial reefs and fish aggregation devices, which have been used previously to facilitate the restoration of damaged ecosystems, and de facto marine-protected areas, which have proven successful in enhancing both biodiversity and fisheries. 5. The deployment of MREI has the potential to cause conflict among interest groups including energy companies, the fishing sector, and environmental groups. Conflicts should be minimized by integrating key stakeholders into the design, siting, construction, and operational phases of the installations, and by providing clear evidence of their potential environmental benefits. 6. Synthesis and applications. MREI has the potential to be both detrimental and beneficial to the environment but the evidence base remains limited. To allow for full biodiversity impacts to be assessed, there exists an urgent need for additional multi and inter-disciplinary research in this area ranging from engineering to policy. Whilst there are a number of factors to be considered, one of the key decisions facing current policymakers is where installations should be sited, and, dependent upon site, whether they should be designed to either minimize negative environmental impacts or as facilitators of ecosystem restoration.