Some firms say they care about the well-being and ‘happiness’ of their employees. But are such claims hype, or scientific good sense? We provide evidence, for a classic piece-rate setting, that happiness makes people more productive. In three different styles of experiment, randomly selected individuals are made happier. The treated individuals have approximately 12% greater productivity. A fourth experiment studies major real-world shocks (bereavement and family illness). Lower happiness is systematically associated with lower productivity. These different forms of evidence, with (...) complementary strengths and weaknesses, are consistent with the existence of a causal link between human well-being and human performance. (shrink)