Fibronectin is an ∼220 kDa (monomer molecular weight) protein that is found in a dimeric soluble form in body fluids, including plasma, and in an insoluble multimeric form as part of many extracellular matrices. It contains binding sites for a wide range of molecules including cell surface receptors such as integrins. It is thought to play an important role in processes that involve cell migration (such as wound healing and development), and emphasizing its importance in embryogenesis, fibronectin null mutations in mice are embryonic lethal (George et al., 1993). In addition to its physiological roles, a number of pathogenic bacteria appear to use fibronectin as a bridge to the host cell surface to adhere to and to invade human cells (Schwarz-Linek et al., 2004). Fibronectin is a modular protein and contains three types of modules that were first identified in fibronectin (fibronectin type I, II, and III modules) and have since been found in other proteins. Traditionally, due to proteolytic stability, fibronectin has been described as containing an N-terminal domain (NTD) (a string of five type I modules; FI) followed by a gelatin binding domain (GBD) (containing type I and II modules, I-II-II-I-I-I) at the N terminus of the molecule and then a string of type III modules making up the central region; there are three more type I modules at the C terminus (Potts and Campbell, 1994). Iain Campbell's laboratory at the University of Oxford pioneered the high-resolution structural characterization of fibronectin modules with the structure of the seventh type I module (determined using nuclear magnetic resonance [NMR] spectroscopy), published in 1990 (Baron et al., 1990). Since then, the structure, dynamics, and ligand-binding of many single modules, module pairs, or larger constructs have been published.