A politician, political leader, or political figure (from Greek "polis") is someone who is involved in influencing public policy and decision making. This includes people who hold decision-making positions in government, and people who seek those positions, whether by means of election, inheritance, coup d'état, appointment, electoral fraud, conquest, divine right, or other means. Politics is not limited to governance through public office. Political offices may also be held in corporations, and other entities that are governed by self-defined political processes.

Public choice theory involves the use of modern economic tools to study problems that are traditionally in the province of political science. (A more general term is "political economy", an earlier name for "economics" that evokes its practical and theoretical origins but should not be mistaken for the Marxian use of the same term.)

In particular, it studies the behavior of voters, politicians, and government officials as (mostly) self-interested agents and their interactions in the social system either as such or under alternative constitutional rules. These can be represented a number of ways, including standard constrained utility maximization, game theory, or decision theory. Public choice analysis has roots in positive analysis ("what is") but is often used for normative purposes ("what ought to be"), to identify a problem or suggest how a system could be improved by changes in constitutional rules. A key formulation of public choice theory is in terms of rational choice, the agent-based proportioning of scarce means to given ends. An overlapping formulation with a different focus is positive political theory. Another related field is social choice theory.