Book excerpt: The party whips are essential components of the U.S. legislative system, responsible for marshalling party votes and keeping House and Senate party members in line. In The Whips, C. Lawrence Evans offers a comprehensive exploration of coalition building and legislative strategy in the U.S. House and Senate, ranging from the relatively bipartisan, committee-dominated chambers of the 1950s to the highly polarized congresses of the 2000s. In addition to roll call votes and personal interviews with lawmakers and staff, Evans examines the personal papers of dozens of former leaders of the House and Senate, especially former whips. These records allowed Evans to create a database of nearly 1,500 internal leadership polls on hundreds of significant bills across five decades of recent congressional history. The result is a rich and sweeping understanding of congressional party leaders at work. Since the whips provide valuable political intelligence, they are essential to understanding how coalitions are forged and deals are made on Capitol Hill.