Migrant networks play an important role in explaining the size and structure ofmigration flows. They affect the private costs and benefits of migration(assimilation channel) and lower legal entry barriersthrough family reunification programs (policy channel). Thispaper presents a micro-founded identification strategy allowing to disentanglethe relative importance of these two channels. Our empirical analysis exploitsUS immigration data by metropolitan area and country of origin. We first findthat the elasticity of migration flows to network size is around one. Moreinterestingly, we show that the policy channel accounted at most for a quarterof this elasticity in the 1990s, and the magnitudes of the total network effectand the policy channel are greater for low-skilled migrants. Our results arestrongly robust to sample selection, identification assumptions, and treatmentfor unobserved bilateral heterogeneity. Furthermore, the policy channel wasstronger in the 1990s than in the 1980s, possibly reflecting the changes in theUS family reunification policies. We conclude that the government capacity tocurb the migration multiplier exists, but is limited.