While Edward B. (‘Ed’) Lewis is famous for his contributions to genetics anddev- opmental biology y, few have read his research papers. One reason for this is availability, man ny having been published in obscure journalsor as book chapters. A second is because his papers in those ?elds are very dif?cult to read. The dif?culty derives from the fact that Lewis has published infrequently, thus manypapers are condensed reviews of man nyyears’ work presented largely in summary form rather than in detail. It is not unusual for the reader to have to infer the experimental methods, even the results, from a few sentences. Furthermore, he often presents his results in terms of abstract models; thus it can be dif?cult to separate the data from the models. Ama ajor goal of this book is to make Lewis’ keypapers accessible to researchers and students. The papers are grouped into several sections that re?ect the changing focus of his research. Each section is preceded by commentary designed to place the papers in historical perspective, with respect to Lewis’ own ideas as well as to those of the larger scienti?c community. The commentaries attempt to highlight the key methods and results—as well as the signi?cance—of each paper by explaining the science in terms that should be understandable to upper-level undergraduates, graduate students and professional researchers.