This research deal with the question of judgment in the work of Hannah Arendt. It represents the incomplete part of her oeuvre and a debated issue in scholarship. The task of the research, then, is twofold: reconstructive and interpretative. The first chapter analyzes Arendt’s reading of Plato and Socrates. In the fifties she develops the conceptual framework of her later account of judgment. Both her reflections on philosophy/politics and on judgment can be considered as attempts to think the relationship between man in the plural and man in the singular. Socrates discovered a mode of philosophizing that did not oppose the life of the thinker and the life of the citizen. Through his figure, she offers an alternative conception of philosophy and its relation to politics. The second section deals with Arendt’s political reading of Kant’s third Critique and suggests a distinction between political, historical and moral judgment, in order to understand the complexity of functions and meanings of the faculty of judgment itself. If the spectator is the man who judges, we can identify different kinds of spectators. This part of the research is concerned with political judgment and challenges the idea that Arendt has two different theories of judgment: while she underlines different aspects of judgment, she never depoliticizes it. Actor and spectator are two complementary modes of relating to common world, rather than mutually exclusive roles. The third chapter focuses on the ethical aspects of Arendt’s work and on moral judgment; it addresses the question of evil, the duality of socratic thinking and its moral effects, the responsibility and the relationship between morality and politics. Once the autonomy involved in moral judgment is seriously taken into account, the conclusive remarks seek to reconsider the category of singularity in relation with plurality in the practice of judgment.