The principles of effective design also had to be brought up to date. Human-centered design (HCD) has emerged since the first edition, partially inspired by that book. This current edition has an entire chapter devoted to the HCD process of product devel- opment. The first edition of the book focused upon making prod- ucts understandable and usable. The total experience of a product covers much more than its usability: aesthetics, pleasure, and fun play critically important roles. There was no discussion of plea- sure, enjoyment, or emotion. Emotion is so important that I wrote an entire book, Emotional Design, about the role it plays in design. These issues are also now included in this edition.
My experiences in industry have taught me about the com- plexities of the real world, how cost and schedules are critical, the need to pay attention to competition, and the importance of multidisciplinary teams. I learned that the successful product has to appeal to customers, and the criteria they use to determine what to purchase may have surprisingly little overlap with the aspects that are important during usage. The best products do not always succeed. Brilliant new technologies might take decades to become accepted. To understand products, it is not enough to understand design or technology: it is critical to understand business.

What has changed? Not much. Everything.
When I started, I assumed that the basic principles were still true, so all I needed to do was update the examples. But in the end, I rewrote everything. Why? Because although all the princi- ples still applied, in the twenty-five years since the first edition, much has been learned. I also now know which parts were diffi- cult and therefore need better explanations. In the interim, I also wrote many articles and six books on related topics, some of which I thought important to include in the revision. For example, the original book says nothing of what has come to be called user experience (a term that I was among the first to use, when in the early 1990s, the group I headed at Apple called itself “the User Experience Architect’s Office”). This needed to be here.
Finally, my exposure to industry taught me much about the way products actually get deployed, so I added considerable infor- mation about the impact of budgets, schedules, and competitive pressures. When I wrote the original book, I was an academic re- searcher. Today, I have been an industry executive (Apple, HP, and some startups), a consultant to numerous companies, and a board member of companies. I had to include my learnings from these experiences.
Finally, one important component of the original edition was its brevity. The book could be read quickly as a basic, general introduction. I kept that feature unchanged. I tried to delete as much as I added to keep the total size about the same (I failed). The book is meant to be an introduction: advanced discussions of the topics, as well as a large number of important but more ad- vanced topics, have been left out to maintain the compactness. The previous edition lasted from 1988 to 2013. If the new edition is to last as long, 2013 to 2038, I had to be careful to choose examples that would not be dated twenty-five years from now. As a result, I have tried not to give specific company examples. After all, who remembers the companies of twenty-five years ago? Who can predict what new companies will arise, what existing companies will disappear, and what new technologies will arise in the next twenty-five years? The one thing I can predict with certainty is that the principles of human psychology will remain the same, which means that the design principles here, based on psychology, on the nature of human cognition, emotion, action, and interaction with the world, will remain unchanged.
Here is a brief summary of the changes, chapter by chapter.

The chapter has one major addition to the coverage in the first edi- tion: the addition of emotion. The seven-stage model of action has proven to be influential, as has the three-level model of processing (introduced in my book Emotional Design). In this chapter I show the interplay between these two, show that different emotions arise at the different stages, and show which stages are primarily located at each of the three levels of processing (visceral, for the elementary levels of motor action performance and perception; be- havioral, for the levels of action specification and initial interpre- tation of the outcome; and reflective, for the development of goals, plans, and the final stage of evaluation of the outcome).