In "The Utility of Force", Rupert Smith expounds his ideas on how to use force efficiently in the modern world, and outlines his view that conflicts today should not be seen through a paradigm of industrial war (as the world wars), but instead through a paradigm of prolonged confrontation (as the war in Afghanistan, or the Bosnian war).
Smith has excellent credentials: He is a retired general who commanded the UN forces in Bosnia in 1995 and has served as Deputy Supreme Allied Commander of NATO. Furthermore, he has clearly done his research for the book properly, and presents many real-world examples throughout the book. Through his examples and arguments, Smith concludes that most states are viewing conflicts through the paradigm of industrial war, and concludes that this leads to an inefficient use of military force. Smith identifies several factors present in many modern conflicts which make the conventional paradigm of industrial war less useful, for example that in many modern conflicts, the enemy is non-state and hard to identify as a cohesive group, and that many modern military operations are set in the context of political goals which are considerably more complicated than simply the defeat of the enemy military forces. He discusses how military intervention should change based on these observations.
All this is interesting and obviously relevant, and provides the fundament for an interesting book. However, the book has a major drawback. Put bluntly, it is simply very long-winded, very academic, somewhat repetitive and often rather boring to read. Also, more than half of the book is basically a history book, discussing the Napoleonic wars, the birth of military theory, the world wars and the cold war, and it is not until page 267 (of 404) that Smith really begins discussing his paradigm in the context of modern conflict proper. This implies that if you are in fact looking for a book about "The Art of War in the Modern World", it will take a good deal of patience on your part before you find what you're looking for.
The ultimate theme of the book - how force can be used efficiently in our modern world - is interesting and important. But the nature of Smith's treatise of the topic unfortunately detracts from the quality of the book, and makes it unnecessarily hard reading.