A new and general model, called the "helical wormlike chain", for both flexible and semi-flexible polymer chains is presented. Statistical-mechanical, hydrodynamic, and dynamic theories of their solution properties are developed on the basis of this model. There are also given analysis of recent experimental data by the use of these theories for flexible polymers over a wide range of molecular weight, including the oligomer region, and for semi-flexible polymers, including biological macromolecules such as DNA. The book includes a reasonable number of theoretical equations, tables, figures, and computer-aided forms, enough to provide understanding of the basic theory and to facilitate its application to experimental data for the polymer molecular characterization.