For more than two decades political scientists have discussed rising elite polarization in the United States, but the study of mass polarization did not receive comparable attention until fairly recently. This article surveys the literature on mass polarization. It begins with a discussion of the concept of polarization, then moves to a critical consideration of different kinds of evidence that have been used to study polarization, concluding that much of the evidence presents problems of inference that render conclusions problematic. The most direct evidence-citizens' positions on public policy issues-shows little or no indication of increased mass polarization over the past two to three decades. Party sorting-an increased correlation between policy views and partisan identification-clearly has occurred, although the extent has sometimes been exaggerated. Geographic polarization-the hypothesized tendency of like-minded people to cluster together-remains an open question. To date, there is no conclusive evidence that elite polarization has stimulated voters to polarize, on the one hand, or withdraw from politics, on the other.

We consider the consequences of the Senate electoral cycle and bicameralism for distributive politics, introducing the concept of contested credit claiming, i.e. that members of a state’s House and Senate delegations must share the credit for appropriations that originate in their chamber with delegation members in the other chamber. Using data that isolates appropriations of each chamber, we test a model of the strategic incentives contested credit claiming creates. Our empirical analysis indicates that the Senate electoral cycle induces a back-loading of benefits to the end of senatorial terms, but that the House blunts this tendency with countercyclical appropriations. Our analysis informs our understanding of appropriations earmarking, and points a way forward in studying the larger consequences of bicameral legislatures.

We have built a country where everyone can choose the neighborhood (and church and news shows) most compatible with his or her lifestyle and beliefs. And we are living with the consequences of this segregation by way of life: pockets of like-minded citizens that have become so ideologically inbred that we don't know, can't understand, and can barely conceive of "those people" who live just a few miles away. (Bishop 2008, 40)

Classical rational choice explanations of voting participation are widely thought to have failed. This article argues that the currently dominant Group Mobilization and Ethical Agency approaches have serious shortcomings in explaining individually rational turnout. It develops an informal social network (ISN) model in which people rationally vote if their informal networks of family and friends attach enough importance to voting, because voting leads to social approval and vice versa. Using results from the social psychology literature, research on social groups in sociology and their own survey data, the authors argue that the ISN model can explain individually rational non-altruistic turnout. If group variables that affect whether voting is used as a marker of individual standing in groups are included, the likelihood of turnout rises dramatically.

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