This thematic issue explores the past, present, and future of UN mediation. Based on in-depth case studies of UN mediation in some of the most intractable contemporary armed conflicts, it shows the challenges related to lacking consensus amongst third parties, disunity in the UN Security Council, and the internationalization of conflicts. At the same time, it highlights the UN’s legitimacy, expertise, and convening power, and its importance in the context of broader international dispute management systems. It also underlines the need to rethink how we measure success of UN mediation efforts and to reflect on the consequences of increasing normative plurality in world politics. Finally, this issue points to some areas for future research, including more critical mediation theory, reflections about the worldviews underlying UN mediation, and innovative approaches related to the UN reform agenda.