Several years ago, Thomas Steitz agreed to contribute a volume to the 'World Scientific Series in Structural Biology' that would deal with the contributions he and his coworkers have made to structural biology during his remarkable career. Sadly, Tom died in the fall of 2018 before he had had time to do more than produce an outline for this book, and a list of the reprints he wanted it to contain.Fortunately, Tom's colleagues and coworkers responded enthusiastically when they were informed later that fall that if they were willing to help out, a volume would be published to commemorate his career. It fell to Anders Liljas, Peggy Eatherton, Tom's longtime administrative assistant, and Peter Moore, a close colleague, to oversee their efforts. Thomas Steitz is best known for the work he and his coworkers did to elucidate the biochemical basis of gene expression. The structures of a large number of the macromolecules involved in transcription and translation emerged from his laboratory over the course of his career. This book includes reprints of the most important papers he had published, grouped according to the structures they relate to, and commentaries written by the scientists who collaborated with him to solve each of them. It thus summarizes the achievements of one of the most distinguished biochemists of the second half of the 20th century.