This paper studies the costs and benefits of the adoption of a
policy of free movement of workers. For countries to agree on uncontrolled
movements of workers, short run costs must be outweighed by the long term
benefits of better labor market flexibility and income smoothing. We show that
such a policy is less likely to be adopted when workers are more impatient and
less risk averse, when production technologies display stronger decreasing
returns and when countries trade a significant share of their products.