Among the most common features of the modern US Congress is its partisanship, a deeply felt political divide that sometimes seems to be each side’s primary motivator. In Congress we have seen heated disagreements, a tendency to blame the opposing party for any bad outcome, and attempts to undermine the other side’s successes. For those watching Congress, it is easy to assume everyone on Capitol Hill participates equally in framing issues as pitting Democrats versus Republicans. Yet in Posting for Power , Jeremy Gelman and Steven Wilson show that partisanship varies a great deal among legislators: it is motivated by reelection and promotion-seeking considerations, and it comes with no substantial legislative or electoral consequences. In the US Congress, lawmakers regularly choose to bicker for political gain, whether or not they disagree on issues. By classifying millions of social media posts as partisan or not, Gelman and Wilson quantify a legislator’s partisan intensity through the time and effort they spend supporting their party and bickering with the opposition. The authors argue that the partisan personas politicians create are both a home style, to help them win reelection, and hill style, to help them become politically influential by showing off as good team players. Bringing together a wide range of data on leadership races, elections, voting records, cosponsorship patterns, and lawmaking outcomes, they demonstrate the nearly consequence-free way that legislators strategically deploy partisanship to impress their copartisans and voters. Gelman and Wilson closely examine what motivates members to differ so much in developing this part of their public personas and offer clear recommendations for how to turn down the partisan heat on Capitol Hill. “This well-written book seeks to explain partisanship in Congress. It makes a strong argument that partisanship is distinct from ideology and develops a novel new measure of partisanship based upon Twitter posts and should be of interest to scholars and students of Congress and political parties.” ― Jacob Smith, Fordham University Jeremy Gelman is Associate Professor of Political Science at the University of Nevada, Reno.  Steven Lloyd Wilson is Associate Professor of Politics at Brandeis University.