The American system of partisan primary elections for the House of Representatives and the Senate is often blamed for contributing to political polarization and conflict in Congress. These concerns have increased in recent decades, as both parties have at times failed to nominate candidates who would have broad general election appeal.This book considers how primary elections have changed over the past decade and why they so often yield extreme or unpopular candidates. It provides detailed studies of how representative primary voters are of the population and how primary candidates plan their campaigns. The book uses this information to determine how reforms such as nonpartisan primaries might affect primary electorates, candidates, and legislators.Collectively, the chapters in this book show that reform of primary election laws could improve the quality of American elections, but we are far from consensus about which reforms would be best or what the effects of existing reform proposals has been. This is the most comprehensive study of contemporary primaries, featuring many of the leading scholars on parties and elections in the United States.