A couple of days ago I got the copy I had ordered of the book "Design Expertise" by Bryan Lawson and Kees Dorst. I have so far only quickly read (skimmed) through the book, but it is obvious that this is one of the best introductions to design theory out there. The authors presents design as a journey. They discuss design from different perspectives, starting out with their notion on how to understand design. They discuss design expertise, how to start your journey to become a designer, what it means to be a professional designer, and how to educate designers.
The theory of design that the authors presents is stable and rests firmly on a deep understanding of design as a basic human activity, and even mroe as a professional activity. Even though the book has architecture as its primary field of design when it comes to examples, the authors do a good job in being open and broad, which means that the book can be read by anyone interested in how to understand design no matter what field.
The book is not a ordinary textbook but at the same time not a fundamental research book. It is in between. For someone who has a good understanding of design and is knowledgeable with many of the original sources the book still offers an integrated understanding of design that is well needed in the field.
After this first read, I have nothing to complain about, however, I will go back and read some parts in more detail, and I will hopefully come back to this preliminary review.
(Of course, I am quite disappointed that the two books on design that I consider to the best so far are not referenced. That is Klaus Krippendorff's "The Semantic Turn - a new foundation for design" and my own "The Design Way" with Harold Nelson :-)