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.