One might think that writing a new edition of an existing book would be a relatively straightforward, if not simple, task. Isn't it just a matter of updating and rearranging a bit, based on reactions of readers of the earlier work? Not according to our experience. But perhaps the problem lies in our approach to new editions. We agreed early on not to settle for a cosmetic touch-up. Instead, we consulted many of those who used the first edition. We asked about what worked and how we could improve the book. We dismantled large parts of the material and carefully reconstructed it, with an eye to producing a clearer and more effective way of learning about biology.