What role, exactly, do skill and luck play in our successes and failures? Some games, like roulette and the lottery, are pure luck. Others, like chess, exist at the other end of the spectrum, relying almost wholly on the skill of the players. But in every other domain-from business, to investing, to sports-skill and luck seem almost hopelessly entangled. In his provocative new book, Michael Mauboussin untangles the intricate strands of skill and luck, defines them, and provides useful frameworks for analyzing their relative contributions.