This book describes the history and present knowledge of a paradigmatic system, the lac operon of E. coli. The first part of the book presents the history of the operon and various schools of thought regarding genetic control in general. The second part presents a number of false interpretations and misconceptions and demonstrates how easily a scientist may deceive himself. The third and last part thoroughly covers the current state of knowledge of the lac operon including the importance of the auxiliary operators and discussions of several X-ray structures, one of which was published shortly before this book went into press. A unique combination of personal anecdotes and present-day science makes this book appealing to students, postdocs, active and retired researchers alike.