This article aims to reinvigorate the utopian imagination as a vital and necessary component in IR theory. Since the First Great Debate between the Realists and the Utopianists (or more accurately, the Liberal-Internationalists) the utopian tradition has been viewed as being both subjective and arbitrary, leading to its dismissal as vain idealism in world politics. This article re-interrogates the arguments of Carr and Morgenthau and finds that they have relevance today only as against closed systems of utopia and have little bearing against the open-dialectical utopianism which is advocated here as a viable alternative to the sterility of realism. The article also examines the historical nexus between realism's dismissal of utopianism and the wider movements in political philosophy via a critical engagement with the works of Popper, Berlin and Arendt. Finally, after exploring the limitations of Booth's idea of 'Utopian Realism', the article argues that utopianism should no longer be assumed to be a blueprint for a future, perfect society, a tradition fraught with the danger of proto-totalisation, but as a critical imaginary that acts as a heuristic device to reveal the fissures in existing reality and as an ideational motivating force for progressive change in world politics.