This special issue of International Organization celebrates the journal's seventy-fifth anniversary. IO was founded in 1946 to document and analyze the role of international organizations in the post-World War II order. The journal focused initially on the United Nations and its specialized agencies but quickly expanded its empirical and analytical scope. Today, IO has become a general interest international relations journal. Yet, questions about how international order, regimes, and institutions shape cooperation and contestation remain at the core of IO's scholarly output.

Much of the international relations scholarship published in these pages has examined aspects of what has come to be called the Liberal International Order. It grew out of an understanding that the post-war era was characterized by ideas and institutions that privileged rule of law, democracy, human rights, the free movement of goods and capital, the multilateral provision of global public goods, and collective security. In this narrative, this order is largely responsible for the unprecedented economic growth and relative peace among economically developed states in the decades after the war. A central question posed in the volume is whether this conception of international order is being challenged and why. Evidence of rising protectionism, inaction on climate cooperation, democratic backsliding, and growing great power conflict all point to an international order under pressure.

It will come as no surprise that authors’ responses to this broad framing are varied. One unifying theme, however, is that the post-war international order was contested among states internationally and among citizens domestically from its beginnings. The order was selectively liberal and applied liberal values inconsistently, whether the question was who was democracy for, whose rights mattered, or which tariffs were liberalized. This selectivity was central to how the order worked. Ignoring liberal values was often essential to achieving the cooperation needed for the wealth and security the system sought to deliver. A number of the contributions in this volume argue that the current pressures on the order are a direct result of expanding the depth and reach of those liberal values after the Cold War. While this theme may be a sobering one, several contributors point out that recognizing how deeply the Liberal International Order has been contested all along also reveals its resilience. Together, the articles present a rich array of views on both the past and future of the institutional order.

IO is first and foremost a community of scholars that has been learning about world affairs together. Our vision for celebrating the journal's seventy-fifth anniversary was to harness the energies of that community. To lead us, we asked David Lake, Lisa Martin, and Thomas Risse to serve as guest editors for this issue. We and the journal owe David, Lisa, and Thomas a deep debt of gratitude for their leadership and intellectual vision.

The guest editors issued a public call for papers in Spring 2018 and received almost 200 proposals. A subset of these were invited for presentation and discussion at a workshop in Madison, Wisconsin, in September 2018. The guest editors invited revisions from a selection of the papers presented at this workshop. These revisions were presented in a second workshop in Berlin, Germany, in June 2019.Footnote ¹ These papers were submitted to IO and evaluated by anonymous reviewers, to whom we are exceptionally grateful. The IO editorial team made the final decision to publish in consultation with the special issue editors.