The honesty of people in an online panel from 15 countries was measured in two experiments: reporting a coin flip with a reward for “heads”, and an online quiz with the possibility of cheating. There are large differences in honesty across countries. Average honesty is positively correlated with per capita GDP. This is driven mostly by GDP differences arising before 1950, rather than by GDP growth since 1950. A country’s average honesty correlates with the proportion of its population that is Protestant. These facts suggest a long-run relationship between honesty and economic development. The experiment also elicited participants’ expectations about different countries’ levels of honesty. Expectations were not correlated with reality. Instead they appear to be driven by cognitive biases, including self-projection.