This thesis presents a new interpretation of the political dimension of Juan Luis Vives's thought by looking at Vives's reception and appropriation of classical rhetoric in the context of northern humanism. This thesis argues that rather than theorizing politics in the language of law, Vives's main contribution to political thought occurred at the intersection of reflections on cognition, rhetoric, and ethical languages of virtuous government. This is to challenge the existing scholarship in two ways. First, it questions a prevalent interpretation of Vives as merely a theoretician of an overarching political concord and peace by showing Vives's deep interest in the possibilities of political action in a postlapsarian world of discord. Secondly, the thesis shows that while Vives, and northern humanism more generally, produced little systematic reflection on some of the basic political and legal concepts, Vives's theorization of cognitive, ethical, linguistic, and educational viewpoints was a way to frame the ultimate conditions and possibilities of political action in a non-utopian world. In the tumultuous 1520s and 1530s, when the religious unity of Christendom and the political concord between different European states were increasingly threatened, Vives argues that language and politics are inseparably entangled on three different levels. First, political, and ethical languages are conceptualized essentially rhetorically; they are meant to be transformative and they have to lead to constructive political action. Secondly and closely connected to the first point, the transformative potential of political discourses must be realized in different practices of counselling linking politics intrinsically to humanist concerns of active life in the service of community. Thirdly, since active life is realized in princely contexts unfavourable to open debate, the use of language and rhetoric has to be appropriated to this new environment. In this process, the place of rhetoric in educational schemes, the internal theory of rhetoric, and the relationship between language and cognition are problematized in the context of wider debates on education, good government, and human freedom central to the northern humanist tradition in the early 16th century. In conceptualizing politics, language, and cognition, largely together Vives's thought points to broader 16th- and 17th-century developments in European political thought where man's nature, passions, and cognition become one of the central concerns of political thought.