Keith T. Poole and Howard Rosenthal have analyzed 16 million individual roll call votes spanning the two centuries since the two Houses of Congress began recording votes in 1789. By tracing the voting patterns of Congress throughout the country's history, Poole and Rosenthal find that, despite a wide array of issues facing legislators, over 80% of a legislator's voting decisions can be attributed to a consistent ideological position ranging from ultraconservatism to ultraliberalism. The authors utilize roll call voting as a framework for a novel interpretation of important episodes in American political and economic history. Using a simple geometric model of voting, Congress demonstrates that roll call voting has a very simple structure and that, for most of American history, roll call voting patterns have maintained a core stability based on two great issues: the extent of government regulation of, and intervention in, the economy; and race. With the exception of the Civil War period, the major political parties have been organized around the issue of government intervention in the economy. Although political parties are the critical element in promoting stable voting alignments, these stable patterns are more than just the result of party alliances. Not only do new stable patterns of voting precede the emergence of new parties, there are also very important distinctions within parties. Race, the second great source of stable voting patterns, has almost always divided the two major parties internally and, in the post World War II era, has split the Democratic party along North-South lines leading to a three-party system. Congress documents the history of race-related issues in Congress and how race has an indirect effect on many other issues such as minimum wages and food stamps. Congress also examines alternative models of roll call voting and finds them lacking. In several detailed case studies, the authors demonstrate that constituency interest or pocket-book voting models fail to account for voting on issues such as minimum wages, strip mining, food stamps, and railroad regulation. Because of its scope and controversial findings which challenge established political and economic models used to explain Congressional behavior, Congress will be essential reading for political scientists, economists, and historians.