A vigorous debate exists about the economic benefits of building a border wall between the US and Mexico. Yet, empirical evidence to guide the debate has lagged behind. This column studies the economic impact of the Secure Fence Act of 2006, which built 550 new miles of fence on the US–Mexico border. At a construction cost of $7 per person, the fence led to a small reduction in migration but had negligible effects on the economy, with high-skilled US workers losing $4.60 per year in income, and low-skilled US workers gaining just $0.36 per year.