Abstract: Theorising about international relations has progressed in recent years, and dialogue between the concurrent disciplines of International Relations, political theory and international law has started to emerge. There is, however, work still to be done in fostering a genuine ‘International Theory’ containing the potential to truly transcend arbitrary disciplinary and methodological boundaries, particularly where the subject matter of the respective disciplines – namely, an inquiry into the means by which a true understanding of the nature and conditions of international relations may be realised – is trans-disciplinary in nature. My thesis seeks to reanalyse the poststructuralist critique of the discipline of International Relations from a contemporary perspective, made possible by the trans-disciplinary progress alluded to above. I choose poststructuralism as a means of considering the most radical attack on the foundations and methodological commitments of traditional IR as I believe the responses which originated from within the discipline – social constructivism in particular – did not go far enough in grounding a robust yet legitimate means by which to construct an understanding of international relations capable of transcending the challenge of poststructuralism. I consider such positions and the constitutive theory of Mervyn Frost in detail before examining the potential of a theoretical amalgamation of the philosophical constructivism of John Rawls with a holistic social constructivist conception of the nature of practical reasoning with norms, as expounded by Friedrich Kratochwil, to ground a ‘completed’ account of normative reasoning capable of overcoming the poststructuralist critique. Finally, I defend the Rawlsian conception of reasonableness (through an analysis of the interpretation afforded such by Peri Roberts) from the charge of overdemandingness levelled at it by Catriona McKinnon. I conclude by claiming that the Rawlsian ideas of reasonableness and public reason can, when combined with Kratochwil’s conception of practical reason, ground a valid response to the challenge of poststructuralism.