The concept of ideology plays a central role in a wide range of political science research. In the fields of public opinion and voting behavior, the study of ideology has charted a somewhat controversial and contentious history. In addition to difficulties with providing even a basic definition for the concept, there has been extensive debate regarding, among other things, what fraction of the public can be said to possess a true ideology, how ideologies are structured, how stable ideologies are over time, and whether ideology has a meaningful effect on various political behaviors. Because of the importance of the concept of ideology to a large body of both theoretical and empirical research, the answers to these questions should be of central interest to American politics scholars. The resolution of these issues is particularly important to the study of spatial voting because this approach sees ideology as the central determinant of vote choice.

This chapter discusses the basic characteristics of the study of political ideology. I begin by describing the various ways in which the term has been defined in the political science literature. Next, I discuss some of the ways that scholars have sought to measure ideology. I then move on to examine the question of how ideological American politics is.