This doctoral thesis argues that, contrary to the appearances of unity, economists are highly disunified in their understanding of central concepts of choice- and game theory, namely, preferences and beliefs. Even though 'preference' is arguably the most central concept in economics and the discipline is very explicit about the structural assumptions that preferences are supposed to satisfy, there is neither an explicit definition of the concept in economic textbooks nor much of a current debate in the discipline. Nevertheless, the last few years have seen the emergence of several views by philosophers of economics concerning what preferences in economics really are (e.g., judgmentalism, various strands of revealed preferences theory). Trying to defend one such story is, in my view, a mistake. Instead, I propose that we should acknowledge that there is significant disunity about concepts like preferences and beliefs in economics, and that explicating this disunity cannot only help us account for important controversies at the forefront of economic research, but also point us towards potential resolutions. As a first step towards my aim, I demonstrate that the various grand narratives about ‘what preferences in economics really are’ fail to account for substantial contributions and practices in economics. I then argue that this is to be expected as only a minimal conception of preferences holds the federation of economics together. This minimal conception is usually enriched with further implicit assumptions that differ across various research programs and are tailored to the specific agendas of the research programs in which they are employed. One of my central claims is that explicating and appraising these more local assumptions will — in contrast to how the debate currently proceeds — allow philosophers of science to contribute substantially to the progress of economics. The thesis supports this claim by looking in detail at i) the disagreements concerning what kind of experiments microeconomics needs and ii) the recent controversy about preference purification in behavioral welfare economics. Concerning the first debate, I argue that proponents of the heuristics-and-bias program usually put internalist restrictions on the constituents of preferences, while proponents of experimental economics in the tradition of Vernon Smith permit agents' environments to play a crucial role in the constitution of their preferences. Regarding the second debate, I argue that disentangling different substantial notions of rationality, which go beyond its technical meaning in economics, can help us account for the vastly different assessments of the plausibility of preference purification in behavioral welfare economics. Turning back to the big picture, my discussion of i) and ii) highlights that economics has more to gain from an explication of the implicit assumptions about choice- and game-theoretic concepts made by different research programs than from overreaching narratives about ‘what preferences really are.’