Spider silks are biological protein polymers which are spun into fibers with an incredibly diverse range of mechanical properties and functions. Spider silks have long been recognized to have mechanical properties that rival most, if not all man-made materials. However, it is not yet possible to make synthetic spider silk fibers that mimic the impressive properties of their native counterparts. This is due in part to the hierarchical nature of spider silk, which introduces a complex organization of structures at nearly every length scale from the atomic to the micron level. The research in this dissertation has been in pursuit of understanding the structure, dynamics and assembly of silk proteins into high performance fibers at the molecular and nanoscale levels. The mechanical properties of a number of spider silks were measured and are discussed and placed intheir biological context. The underlying molecular interactions that give rise to these fibers are investigated by DLS, cryo-TEM, solution and solid-state NMR. The solution NMR work combined with cryo-TEM illustrates that silk proteins are stored as protein pre-assemblies in the silk gland and are the fundamental precursors to silk fibrils. The application of denaturant was used to disrupt these protein superstructures and understand the forces and dynamics that facilitate assembly. Finally, solid-state NMR was used to structurally characterize prey wrap spider silk, the toughest of the spider silks, and illustrate its α-helical coiled-coil hierarchical structure that helps explain this silk’s high extensibility and impressive mechanical performance.