On the Citizen is both the second version of Hobbes’s political theory, a precursor of Leviathan, and part of a scientific project titled “The Elements of Philosophy.” The chapter disentangles how the work relates to these different contexts. It examines the development of Hobbes’s political thinking by comparing On the Citizen with an earlier text (The Elements of Law), giving particular attention to his discussions of the state of nature, the political covenant, and governmental accountability. Turning to the second context, the chapter tracks the evolution of Hobbes’s thinking away from purely formal, definitional science. On the Citizen lays out the problem of the contestability of foundational concepts in moral and political philosophy and tries out a solution in the form of a concept of “right reason.” Alongside that ultimately unsatisfactory line of thinking, Hobbes also advances an empirical approach to science of a more political nature. As indicated by the title, On the Citizen was framed to cover political subjects, an empirical focus that propelled Hobbes’s development as a political theorist. Leviathan is a master work in political theory because it was preceded by On the Citizen.