A large-scale randomized experiment conducted during the 2012 French presidential and parliamentary elections shows that voter registration requirements have significant effects on turnout, resulting in unequal participation. We assigned 20,500 apartments to one control or six treatment groups that received canvassing visits providing either information about registration or help to register at home. While both types of visits increased registration, home registration visits had a higher impact than information-only visits, indicating that both information costs and administrative barriers impede registration. Home registration did not reduce turnout among those who would have registered anyway. On the contrary, citizens registered due to the visits became more interested in and knowledgeable about the elections as a result of being able to participate in them, and 93% voted at least once in 2012. The results suggest that easing registration requirements could substantially enhance political participation and interest while improving representation of all groups.