PREFACE With the advent of increasingly robust technologies that provide cellular and organismal views of molecular processes, progress in biochemistry continues apace, providing both new wonders and new challenges. The image on our cover depicts an active spliceosome, one of the largest molecular machines in a eukaryotic cell, and one that is only now yielding to modern structural analysis. It is an example of our current understanding of life at the level of molecular structure. The image is a snapshot from a highly complex set of reactions, in better focus than ever before. But in the cell, this is only one of many steps linked spatially and temporally to many other complex processes that remain to be unraveled and eventually described in future editions. Our goal in this seventh edition of Lehninger Principles of Biochemistry, as always, is to strike a balance: to include new and exciting research findings without making the book overwhelming for students. The primary criterion for inclusion of an advance is that the new finding helps to illustrate an important principle of biochemistry. With every revision of this textbook, we have striven to maintain the qualities that made the original Lehninger text a classic: clear writing, careful explanations of diffi cult concepts, and insightful communication to students of the ways in which biochemistry is understood and practiced today. We have coauthored this text and taught introductory biochemistry together for three decades. Our thousands of students at the University of Wisconsin–Madison over those years have been an endless source of ideas on how to present biochemistry more clearly; they have enlightened and inspired us. We hope that this seventh edition of Lehninger will, in turn, enlighten current students of biochemistry everywhere, and inspire all of them to love biochemistry as we do.