Polyurethanes are among the most commercially significant specialty polymers, with an annual production volume of 25 million metric tons. Their manufacturing process utilizes liquid reactive components, and the wide variety of starting materials enables the creation of a diverse range of products for the consumer, transportation, industrial, and construction industries. This book discusses the synthesis of isocyanates and polyols, along with their polymerization, linking the structures of the starting components to the polymer morphology and mechanical properties of the resulting polymers. It provides a fundamental introduction to polymer physics, processing, and foam formation while focusing on three main applications of polyurethane: low-density rigid foam, low-density flexible foam, and elastomers. The book is suitable for graduate students in chemistry, materials science, and industrial chemistry, as well as for those new to the polyurethanes industry.