The literature in polymerization reaction engineering has bloomed sufficiently in the last several years to justify our attempt in putting together this book. Rather than offer a comprehensive treatment of the entire field, thereby duplicating earlier texts as well as some ongoing bookwriting efforts, we decided to narrow down our aim to step growth polymerization systems. This not only provides us the lUxury of a more elaborate presentation within the constraints of production costs, but also enables us to remain on somewhat familiar terrain. The style and format we have selected are those of a textbook. The first six chapters present the principles of step growth polymerization. These are quite general, and can easily be applied in such diverse and emerging fields as polymerization applications in photolithography and microelec- tronics. A detailed discussion of several important step growth polymeriz- ations follows in the next five chapters. One could cover the first six chapters of this book in about six to eight weeks of a three-credit graduate course on polymerization reactors, with the other chapters assigned for reading. This could be followed by a discussion of chain-growth and other polymeriz- ations, with which our material blends well. Alternately, the entire contents of this book could be covered in a course on step growth systems alone.