Abstract This chapter explores legal knowledge and expertise as a driving force in international governance systems. In particular, it analyses the agency of legal experts in international law and politics. The chapter starts out by emphasizing the growing power of international adjudicatory institutions, before theorizing legal expertise and knowledge in international politics and governance as forms of professional capital. The chapter then turns to empirical illustrations of how jurists and networks of legal experts function as transnational power brokers in international politics and governance. We draw on examples from our own empirical work on international adjudicatory institutions that deal with atrocity crimes and human rights violations, two areas marked by inherent tensions between law and politics, to demonstrate how legal expertise is an essential part of international governance. The chapter shows how legal knowledge and expertise, at specific critical junctures, affected the creation of new international adjudicatory institutions, their legal frameworks, and normative goals. Often employed in top positions in these institutions, elite jurists were later able to give direction to the development of new legal concepts and practices that helped shape the space in which international politics unfolds.