In the marine environment, mussels anchor to stable surfaces with a beard-like filament network called “byssus”. Mussels usually reside in intertidal rocky zones where current, tides, and waves threaten their dislodgment. In response to this environmental pressure, byssus threads have a unique combination of strength and extensibility only surpassed by silk. The mechanical properties of these protein fibers are conferred by a complex architecture involving collagen, histidine, silk, elastin and plant cell wall domains, held together by disulfide bridges and metal cross-linking. This seminar will present how, using 13C nuclear magnetic resonance (NMR) experiments and isotopically-enriched byssus threads, we are able to study the molecular structure and dynamics of these high-performance fibers. First, we have refined the structural model by obtaining information at the molecular level of the amino acids’ environment using two-dimensional and chemical shift prediction. Mussels are exposed to water and air following the cycle of the tide, and the mechanical properties of byssus threads change drastically with their hydration state. We have thus also studied the dynamical changes resulting from the slow dehydration of the fibers. We propose a mechanical model responsible for the shock-absorbing properties and extensibility of the fibers.