The left-right political divide is among the most contentious in modern society, often eliciting more explicit acrimony than divisions based on race, religion, or social class. In this dissertation, I present three lines of research examining the ideological divide. This work illustrates the three main lenses through which I have approached the study of ideology, examining its causes, correlates and consequences. In the first series of studies I focus on the upstream causes of ideology, examining how individual differences in low-level physiological traits can influence a person’s political attitudes. In four studies (total N = 1,639) I provide evidence that genetically determined differences in gustatory (taste) sensitivity shape a person’s political ideology, with more taste-sensitive individuals tending to become more politically conservative. In the second line of research, I turn to the correlates of ideology, investigating how the same upstream factors that influence ideology can also shape other aspects of cognition for those on the left and right. In a series of 14 studies (total N = 4,595), I find that there are wide-ranging ideological differences in judgment and decision-making confidence, with political conservatives exhibiting greater metacognitive confidence across a broad range of judgment domains. I also find evidence that these differences in confidence are driven by the same upstream epistemic needs that shape political ideology. Finally, I consider the downstream consequences of ideology, examining how belonging to an ideological group, in turn, can influence a person’s cognition and behavior. In a series of 12 studies (total N = 9,917), I examine how shifting social norms among ideological ingroups reshaped Americans’ intergroup attitudes in the wake of the 2016 U.S. Presidential Election. I find evidence that Donald Trump’s political ascent substantially reshaped expressions of explicit prejudice among Americans—but that the direction of this change diverged sharply along ideological lines: conservatives (especially Trump supporters) showed significant increases in prejudice towards a wide range of minority groups. Liberals, conversely, showed significant decreases in prejudice over this same period. In conclusion, I consider some possible future research directions at the intersections of these three lines of work.