A new and general model, called the "helical wormlike chain," for both flexible and semiflexible polymer chains is presented. Statistical-mechanical, transport and dynamic theories of their solution properties are developed on the basis of this model. An analysis is given of recent experimental data using these theories for flexible polymers covering a wide range of molecular weights, including the oligomer region, and for semiflexible polymers, as well as biological macromolecules such as DNA. The book includes many theoretical equations, tables, figures, and computer-aided forms, to provide an understanding of the basic theory and to faclitate its application to experimental data for polymer molecular characterization.