Pay transparency policies are increasingly popular among governments in the United States and around the world. For instance, many European countries require large employers to report gender-disaggregated pay statistics, and most U.S. states make the salaries of state employees available to the public. I summarize a growing body of academic work measuring the effects of transparency policies. These studies reveal that certain policies had the intended effects, such as reducing gender pay gaps. On the other hand, there is growing evidence of undesired effects. I conclude with policy recommendations and avenues for future research.