The title of this chapter refers most broadly to the understanding of man as a being who ‘acts’, or who does things in society, as opposed to an understanding of man as a being who is defined fundamentally by his capacity for thought and reasoning. Arendt thought that, in the modern world, man had come to be defined as an acting rather than a thinking being, and that this definition of him formed a key aspect of the modern world’s break with tradition. This chapter will seek to understand why, according to Arendt, man’s action has become fundamentally meaningless in modern society. Unlike many of her contemporaries, who we will compare her with in this chapter, Arendt did not think that acting in society was inherently meaningless, or that it was impossible for social actors to act in a meaningful way. She took political revolution to be a key example of how action can, under the right conditions, become meaningful in society (see Chapter 1). For Arendt, the question of the meaning of action is tied to the question of what makes a meaningful politics. Arendt’s effort to recover a sense of what meaningful social action might be like also led her to consider a more specific type of ‘acting’ – that is, acting on the stage, in the theatre. The theatre has been used throughout history by philosophers as a metaphor for the fundamental meaninglessness and futility of human action. In this chapter we will look at how Arendt sought to turn the philosophical understanding of the theatre inside out, and to use the example of the theatre as a guide in her effort to understand what meaningful action might be like.