There are a fair number of books on this subject, but for my money only 2 are really worth getting: Bruce Jentleson's "American Foreign Policy" and this text.
I am a professor at an I.R. Department of a university, so naturally I am always on the look out for any new and good book on US foreign policy, as that is one of the courses that I usually teach. This comprehensive text is really a blessing for anyone engaged in either teaching the subject or being a student of it.
The book is an indepth study of US foreign policy of the last 200 years or so, with clear emphasis placed on the more recent area, namely the Cold War and beyond. At 670 pages it is certainly not short, but so far I can only say that just about everything is relevant to the subject. The main authors of this text Wittkopf and Kegley can certainly be considered veterans of this subject. Their approach is not only pervasive but also insightful. There are numerous examples and the sources explored are very relevant and important, as far as I could tell. The authors go through all the different aspects of US foreign policy and have a chapter on decision making as well. Models and theories are also briefly discussed, although this is not a theory book.
To make a long story short, this is certainly a text book worth having for the student of US foreign policy and I.R.