Cereal and plant proteins are used frequently in the manufacture of animal, fish and human food products but are often deficient in essential amino acids. In contrast, macroalgal proteins contain all the essential amino acids and are a rich source of other bioactives including taurine, lipids, carotenoids and pigments. Furthermore, macroalgal proteins are a substrate for bioactive peptides generation. This paper discusses macroalgal bioactives and their potential use in fish, animal and human nutrition and health. Issues including their safe use, sustainability of supply, efficient drying and processing methods and novel extraction technologies are discussed as well as legislation issues.