Many fish species are threatened worldwide by overfishing, contamination, coastal development, climate change, and other anthropogenic activities. Marine renewable energy (MRE) is under development as a sustainable alternative to carbon-based energy sources. Regulators and stakeholders worry that MRE devices will add another threat to fish populations already under pressure. This paper reviews the current knowledge of potential effects of MRE development on fish. These may include collision with devices that may lead to injury or death; underwater noise generated by MRE devices that may affect fish behavior and health; electromagnetic fields from power cables and other electrical infrastructure that may lead sensitive fish species to approach or avoid them; changes in critical fish habitat, including nursery, feeding, and spawning grounds; shoaling of fish around MRE devices; and displacement of fish populations or communities around arrays of multiple MRE devices. Field- and laboratory-based studies that have examined fish presence, avoidance, and evasion around MRE devices suggest that collisions are rare. Progress is being made on data collection and modeling tools to estimate fish encounter rates with MRE devices, the consequences of collisions, and population-level ecological risks. Similarly, studies exposing fish to turbine-generated noise and electromagnetic fields demonstrate little effect on fish behavior; in fact, MRE device noise falls below reported hearing thresholds. Inquiries into the effects of MRE devices on fish are ongoing, and research is needed to ensure the health of fish populations while facilitating the sustainable development of renewable energy sources.