This book provides a presentation of Jürgen Habermas' oeuvre, with particular reference to his theory of communicative action. It formulates the concepts of communicative rationality and validity claims, indicates the conditions of a perfect communicative rationality, and underscores Habermas' distinction between understanding- and success-oriented actions. Moreover, this book considers Habermas' critical reception of classical sociologists such as Weber and Durkheim; of the Lukacs and Frankfurt school; of Schutz, Mead, and Wittgenstein; and of important contemporary authors such as Foucault, Parsons, and Luhmann. Segre also explores Habermas' themes of the rationalization of the life-world and its consequences on the social, cultural, and personality systems. He discusses Habermas' well-known theses of colonization of the life-world, its impact on the public sphere and communicative action, and the legitimacy crisis that follows as a consequence.