Book excerpt: "What The Double Helix did for biology, David Warsh's Knowledge and the Wealth of Nations does for economics." —Boston Globe A stimulating and inviting tour of modern economics centered on the story of one of its most important breakthroughs. In 1980, the twenty-four-year-old graduate student Paul Romer tackled one of the oldest puzzles in economics. Eight years later he solved it. This book tells the story of what has come to be called the new growth theory: the paradox identified by Adam Smith more than two hundred years earlier, its disappearance and occasional resurfacing in the nineteenth century, the development of new technical tools in the twentieth century, and finally the student who could see further than his teachers. Fascinating in its own right, new growth theory helps to explain dominant first-mover firms like IBM or Microsoft, underscores the value of intellectual property, and provides essential advice to those concerned with the expansion of the economy. Like James Gleick's Chaos or Brian Greene's The Elegant Universe, this revealing book takes us to the frontlines of scientific research; not since Robert Heilbroner's classic work The Worldly Philosophers have we had as attractive a glimpse of the essential science of economics.