The elections system in the U.S. is highly decentralized, with individual states responsible for administering state and federal elections. As a result, states vary in their voting regulations, and in particular, whether or not an ID is requested or required to be presented at the voting booth. Election security has been cited as a reason for implementing voter ID laws. However, they also introduce additional barriers to voting, which may lower voter turnout.
This is an addendum to a previous Science Note on Voter Fraud.