"Notions of openness are increasingly visible in a great number of political developments, from activist groups, software projects, political writings and the institutions of government. And yet, there has been very little reflection on what openness means, how it functions, or how seemingly radically different groups can all claim it as their own. Openness, it seems, is beyond disagreement and beyond scrutiny. This article considers the recent proliferation of openness as a political concept. By tracing this (re)emergence of ‘the open’ through software cultures in the 1980s and more recently in network cultures, it shows how contemporary political openness functions in relation to a new set of concepts – collaboration, participation and transparency – but also identifies important continuities with previous writings on the open, most notably in the work of Karl Popper and his intellectual ally Friedrich Hayek. By revisiting these prior works in relation to this second coming of the open, the article suggests that there is a critical flaw in how openness functions in relation to politics, beginning with the question: How is that new movements championing openness have emerged within a supposedly already-open society?"