The notion of a `rational consensus' is an essential feature of Jürgen Habermas's discourse-based theories of truth and rightness. Although he has somewhat toned down his earlier stress on consensus in recent years, the notion remains of great importance for his account of `understanding' that is at the heart of his formal pragmatic approach to the problem of meaning. My thesis is concerned with that approach and whether Habermas succeeds in building a sustainable theory of truth and rightness on its basis. I start off by trying to elucidate the crucial notions of `the lifeworld', `communicative action' and `formal pragmatics'. I explore Habermas's pragmatic conception of understanding and its relation to the formal semantic account of meaning in terms of the truth conditions of sentences. In the second part of my thesis, I introduce Habermas's early `consensus theory' of truth and rightness and mention some of the criticisms that theory has provoked. I then focus on his revised 'janus-faced' account of truth and show how it overcomes some of the shortcomings of his earlier theory. I then raise some critical points about the revised approach, and go on to point out a fundamental difficulty any account of truth and meaning that incorporates the notion of a `rational consensus' faces. I try to overcome that difficulty by attempting to incorporate some kind of meaning holism into Habermas's pragmatics. The third part of this thesis is concerned with the practical consequences of the pragmatic notion of understanding. I examine what exactly the implications of formal pragmatics are for discourse ethics, and argue that there arises a problem in connection with the distinction between discourses of justification and discourses of application. Finally, I look at the relation between understanding and impartiality, and compare Habermas's account of impartiality as tied to a `rational consensus' with Rawls's notion of impartiality that draws on an `overlapping consensus'. In a last step, I argue that the various difficulties that arise in the context of Habermas's pragmatic approach to truth and rightness and are ultimately due to an overburdening of the notion of understanding and (intersubjective) agreement. I end up suggesting that in the light of these problems, we should be interested in the notion of `rational disagreement'. I offer some very cursory remarks as to how one might go about an enquiry into that notion.