Voter-identification laws (“voter ID laws”) have provoked a fierce controversy in politics and public law. Supporters claim that such laws deter fraudulent votes and protect the integrity of American elections. Opponents, on the other hand, argue that such laws, like poll taxes and literacy tests before them, intentionally depress turnout by lawful voters. A vast literature, including legal scholarship and opinions by the Supreme Court, accept these two narratives. But these narratives are wrong, or at least incomplete. Voter ID laws can have many effects, including surprising ones, like this: They can exacerbate fraud. To illustrate, suppose that without a voter ID law candidates A and B would receive 13 and 10 lawful votes, respectively, and B would receive 2 fraudulent votes. Candidate A wins nonfraudulently, 13 to 12. Now suppose that with a voter ID law, candidates A and B would get 9 and 9 lawful votes, respectively (less than before because of depressed turnout), and B would get 1 fraudulent vote (less than before because of fraud deterrence). Candidate B wins fraudulently, 10 to 9. The conditions necessary for voter ID laws to have this effect are simple and may be common. This Essay captures this risk with a formula, the Election Integrity Ratio, which judges and scholars could use to determine when voter ID laws protect elections—and when they cause the very problem they purport to solve. This Essay has implications for constitutional law and public policy. It also has broad reach: Any law that deters fraudulent votes, depresses lawful votes, or does both—such as citizenship and residency requirements, which are used throughout the United States and around the world—is subject to the analysis herein.