In many countries (including the US) citizens must register before voting. This paper provides experimental evidence on the impact of this additional hurdle on the size and composition of the electorate. Prior to the 2012 French presidential and parliamentary elections, 20,500 households were randomly assigned to one control or six treatment groups. Treatment households received home canvassing visits providing either information about registration or help to register at home. The authors show that France's registration requirements have significant effects on turnout and disproportionately discourage marginalized citizens on the left of the political spectrum. While both types of visits increased registration and turnout, the home registration visits had a higher impact than the information-only visits, indicating that both information costs and administrative costs are barriers to registration. Visits paid closer to the registration deadline were also more effective, suggesting that registration requirements' effects are reinforced by procrastination. The authors' design allows them to distinguish selection and treatment effects of home registration. They find that home registration included additional citizens who were only slightly less likely to vote than those who would have registered anyway, and did not reduce turnout among the latter. On the contrary, citizens induced to vote due to the visits also became more interested in the elections. Overall, these results suggest that the reduction of registration requirements could substantially increase political participation and improve representation of marginalized groups without debasing the average level of competence and informedness among voters.