Small angle scattering experiments with neutrons (SANS, USANS) and light (SALS) are used to probe the structure of fibrin networks (blood clots) over a broad range of length scales (1-20,000 nm). SANS probes the rich internal structure of the fibers (protein arrangement, fiber porosity) while USANS and SALS provide valuable information on the structure of the bifurcating fibrin network (e.g. correlation length). In our experiments, we are also able to probe the mechanical properties (rheology) of the clots while simultaneously obtaining structural information through scattering. This allows us to correlate the structure of these important materials to their unique elastic and strain-hardening properties. Furthermore, we also discuss changes occurring in fibrin networks that are formed under flow. It is found the polymerization of the network in a shearing environment results in significant alterations of its structure and rheology.