This is the third edition of the book, much expanded to include and incorporate important developments in the subject over the last fifteen years. The book represents a comprehensive treatise on all aspects of the bainite transformation, from the choreography of atoms during the phase change to length scales that are typical of engineering applications. The alloy design that emerges from this explains the role of solute additions, and the pernicious effects of impurities such as hydrogen. The picture presented is self-consistent and therefore is able to guide the reader on the exploitation of theory to the design of some of the most exciting steels, including the world's first bulk nanostructured metal.