Joint custody following divorce is widespread, yet the implementation of joint custody is costly when individuals live in different states, so it affects interstate mobility. Migration of divorced fathers has fallen significantly more than that of married fathers. We show the causal effect of joint custody using two strategies. First, we survey divorced parents to elicit beliefs about the likelihood of interstate moves. Second, we use the staggered adoption of joint custody laws across U.S. states, and show a reduction in actual migration of 11 percentage points for fathers. For mothers, there is no impact on mobility from the adoption of joint custody, though there is suggestive evidence of beneficial labor market outcomes.