The byssus is a holdfast structure that allows the marine mussel ( Mytilus) to adopt a sessile mode of life even in the most wave- swept habitats. The success of byssus as an adaptation for attachment is at least in part responsible for the fouling caused by these organisms, but it has also provided inspiration for the design of underwater adhesives and coatings. A valuable bio- inspired concept emerging from mussel adhesion is that of polymers with catecholic and phosphate functionalities for robust underwater surface coupling. Prepolymer processing by complex coacervation for good spreading and functional gradients is also likely to find applications.