We live in a gambling age. Many millions of people play the lottery, speculate on the stock market, gamble on the internet. In times of recession, bookmakers, like hairdressers and preachers, flourish. And the one thing that unites all gamblers, in every form, at whatever stakes, is their belief in luck. Every card player knows that luck exists, and it runs in streaks. But what is luck? We use the idea of it in situations where we cannot control all the circumstances. Is it an actual force that intervenes between desire and its consummation, either impeding that consummation or promoting it? Or is it just the word that is loosely used for a brief anomaly when the desired (or dreaded) outcome occurs less or more frequently than probability suggests it should? Part history of the notion of luck, this is also a history of the psychology of luck and a picture of our gambling age.