The Filer Voter experiment assessed the effectiveness of conducting voter registration drives at sites providing free income tax preparation assistance to low-and moderate-income households in Cleveland, OH, and Dallas, TX. We find that the program doubled the likelihood of unregistered tax filers registering to vote, and that new registrants voted in the following election at slightly higher rates than the state average. Moreover, the program did not measurably slow the tax preparation process. If the experience of the Filer Voter pilot programin Dallas and Cleveland were replicated at VITA programs nationwide, we would expect about 115,000 unregistered eligible voters to register to vote, including 63,000 people who would not otherwise register. These results indicate that the Filer Voter model has substantial potential to increase civic engagement at low cost to voters, tax preparers, and government institutions.