This paper analyzes the factors influencing whether countries become tax havens. Roughly 15% of countries are tax havens; as has been widely observed, these countries tend to be small and affluent. This paper documents another robust empirical regularity: better-governed countries are much more likely than others to become tax havens. Controlling for other relevant factors, governance quality has a statistically significant and quantitatively large association with the probability of being a tax haven. For a typical country with a population under one million, the likelihood of a becoming a tax haven rises from 26% to 61% as governance quality improves from the level of Brazil to that of Portugal. Evidence from US firms suggests that low tax rates offer much more powerful inducements to foreign investment in well-governed countries than do low tax rates elsewhere. This may explain why poorly-governed countries do not generally attempt to become tax havens, and suggests that the range of sensible tax policy options is constrained by the quality of governance.