There has been a substantial increase in research on the determinants and consequences of political ideology among political scientists and social psychologists. In psychology, researchers have examined the effects of personality and motivational factors on ideological orientations as well as differences in moral reasoning and brain functioning between liberals and conservatives. In political science, studies have investigated possible genetic influences on ideology as well as the role of personality factors. Virtually all of this research begins with the assumption that it is possible to understand the determinants and consequences of ideology via a unidimensional conceptualization. We argue that a unidimensional model of ideology provides an incomplete basis for the study of political ideology. We show that two dimensions—economic and social ideology—are the minimum needed to account for domestic policy preferences. More importantly, we demonstrate that the determinants of these two ideological dimensions are vastly different across a wide range of variables. Focusing on a single ideological dimension obscures these differences and, in some cases, makes it difficult to observe important determinants of ideology. We also show that this multidimensionality leads to a significant amount of heterogeneity in the structure of ideology that must be modeled to fully understand the structure and determinants of political attitudes.