Significant progress has been made recently in the determination of the structure and assembly of the important matrix protein fibronectin, a molecule mainly constructed from three modular units denoted Fn1, Fn2 and Fn3. Atomic resolution structures are now available for all three single modules, for Fn1 and Fn3 module pairs, and for the disulphide-linked join between fibronectin monomers. Combined with results from new binding and mutation studies, the new structural information is leading to a clearer view of structure/function relationships in intact fibronectin.