We investigate how board overlap affects coordination and performance among public firms. Our identification exploits the staggered introduction of Corporate Opportunity Waivers (COWs) in nine U.S. states since 2000. By reducing legal risk to directors serving on multiple boards, the COW legislation increased intra-industry board overlap for those firms that benefit most from the information flow facilitated by board overlap. We find that more board overlap improves firm profitability but also reduces investment, product overlap, and innovation. Our findings support the notion that board overlap curtails firm rivalry.