Before the application of small-angle neutron scattering (SANS) to the study of polymer structure, chain conformation studies were limited to light scattering and small-angle x-ray scattering (SAXS) techniques. These experiments were usually conducted in dilute solution, and the methodology to measure radii of gyration, virial coefficients, molecular weights, etc., was well established in the classical works of Guinier, Zimm, Debye and Kratky, who pioneered these techniques during the 1940s and 1950s. This methodology could not be applied to concentrated solutions or bulk polymers because of the difficulty of separating the intra- and inter-molecular components of the scattering function. One attempt to circumvent this difficulty was the experiment by Krigbaum and Godwin, who end-labeled polystyrene molecules with Ag atoms. When dispersed in unlabeled polystyrene, the excess x-ray scattering could in principle be analyzed to provide the end-to-end distance, though in practice the signal-to-noise ratio of the experiment was insufficient for accurately determining this parameter. To our knowledge the first suggestion to use the difference in coherent scattering lengths of deuterium (bD = 0.66 × 10−12cm) and hydrogen (bH = −0.37 × 10−12cm) to create scattering contrast between deuterated and normal (hydrogenous) molecules and provide a direct determination of molecular dimensions was made independently by at least two groups in the late 1960s. By deuterating the whole molecule, as opposed to end-labeling, this proposal increased the signal-to-noise ratio of the experiment by several orders of magnitude and made possible for the first time the practical analysis of molecular conformations in bulk polymers. Even so, such experiments could not be undertaken until the completion in Europe of the first instruments employing long wavelength neutrons and large distances between the entrance slit, sample and detector, which allowed deuterium labeling methods to be successfully applied to polymers in the early 1970s.