Over the past two decades, the study of emotions has emerged as a transformative frontier within International Relations (IR). The Oxford Handbook of Emotions in International Relations aims to capture and contextualize these developments, highlighting how the analysis of emotions has allowed for deeper understandings of international and global politics. The handbook provides a systematic overview, mapping an inherently multi-disciplinary field. Contributions to the volume reveal that emotions are implicated in a variety of processes and practices in IR-including diplomacy, security and conflict, global governance and law, and transnational politics. The chapters trace the evolution of emotion in IR from “first wave” research on emotions as irrational impulses disrupting decision-making at moments of crisis to “second wave” contributions seeking to investigate the manifold roles emotions play in shaping state behavior and global interactions in practice. The handbook showcases recent scholarship on the influence of emotions across many areas, including human rights and humanitarianism, peace negotiations, transitional justice, climate change, financial crises, political protest, populist movements, and immigration. Through these investigations, the volume offers innovative insights and opens up new questions for the field. Rather than merely asserting that emotions matter, the handbook demonstrates how an analytical focus on emotions can challenge assumptions about rationality and reveal deeper complexities in world politics.