The development of marine renewable energy (MRE; offshore wind, tide and wave energy) in Scottish waters and elsewhere has given rise to concerns about the potential impacts of such technologies on the marine environment. One such potential impact of marine renewable energy development is the risk of whales, basking sharks and other large animals (“marine megafauna”) becoming entangled in mooring systems and associated power cables. Similar entanglements in fishing gears have long been recognised as a significant global cause of injury and mortality for many species, and there are concerns that future expansion of the MRE industry may exacerbate the risk. In the current absence of large numbers of MRE-associated moorings, there are few concrete data on which to base an assessment of entanglement risk. A comprehensive literature review confirmed that the vast majority of marine megafauna entanglement records worldwide involved fishing gear. There were, however, several reports of large whales interacting with (or becoming entangled in) anchor chains, aquaculture moorings and similar structures, sometimes leading to injury or mortality. This evidence suggests that moorings, such as those proposed for MRE devices, will likely pose a relatively modest risk in terms of entanglement for most marine megafauna, particularly when compared to entanglement rates in fisheries. Nevertheless, some circumstances were identified under which moorings associated with MRE devices could pose a risk to marine megafauna, particularly 1) in cases involving baleen whales and 2) if derelict fishing gears become attached to the mooring and continue to fish, thereby creating an entanglement risk for a wide range of species (including fish and diving seabirds).