Mussels (Mytilus edulis and related species) are farmed in enormous quantities globally, with annual production exceeding 1.8 million tonnes. The welfare status of mussels is deeply uncertain: they lack a centralised brain and nociceptors in the vertebrate sense, but show nociceptive responses to noxious stimuli and have been proposed as potentially sentient by some researchers. The London School of Economics 2021 report on animal sentience concluded that evidence for mussel sentience was not sufficient to warrant precautionary welfare consideration, while noting ongoing scientific debate. Welfare-relevant harvesting practices include air exposure during handling, temperature extremes, and cooking alive. The vegan and animal welfare community is divided on mussel consumption ethics. Welfare-conscious aquaculture guidelines for mussels focus on minimising prolonged air exposure and thermal stress during harvest and transport. Research into mussel nociception and stress physiology continues.