Since its first appearance fifteen years ago, 'Why Parties?' has been essential reading for anyone wishing to understand the nature of American political parties, but in the interim, the party system has undergone some radical changes. In this landmark book, now rewritten for the new millennium, John H. Aldrich goes beyond the clamor of arguments over whether American political parties are in resurgence or decline and undertakes a wholesale reexamination of the foundations of the American party system. Surveying critical episodes in the development of American political parties - from their formation in the 1790s to the Civil War - Aldrich shows how they address three fundamental problems of democracy: how to regulate the number of people seeking public office, how to mobilize voters, and how to achieve and maintain the majorities needed to accomplish goals once in office. Aldrich brings this innovative account up to the present by looking at the profound changes in the character of political parties since World War II, especially in light of ongoing contemporary transformations, including the rise of the Republican Party in the South, and what those changes accomplish, such as the Affordable Care Act. Finally, 'Why Parties?' offers a fuller consideration of party systems in general, especially the two-party system in the United States, and explains why it is necessary for effective democracy.