Presents the state-of-the-art in molecular weight distribution of polymeric materials. First chapter covers the concepts of molecular averages and distribution functions for polydisperse polymer systems. Chapters 2 through 4 summarize techniques for determining number average molecular weight. Following chapters cover all the modern techniques for determining molecular weight, including classical light scattering, x-ray scattering, neutron scattering, use of the ultracentrifuge, viscometric determination, viscoelastic measurements, fractionation techniques, chromatographic techniques, mass spectrometry, as well as methods for characterizing insoluble polymers. Final chapter surveys the various types of standard polymers available for commercial sources.