This course operates at the nexus of public international law, politics of international law, history of legal and political thought, and intellectual history. It aims at deepening our understanding of international law by exploring the intellectual foundations of contemporary international law. Without knowledge of the origins of international law and the various theoretical approaches in its regard, today's prevailing concepts and principles are hard to understand and alternatives for the future are difficult to grasp. Each week we read texts by historic as well as contemporary scholars - from Grotius, Hobbes, Leibniz, Kant, and Hegel, to the early twentieth century scholars, such as Hans Kelsen, Hersch Lauterpacht and Inis Claude, to today's 'post-modernist' or critical legal scholars, such as Anthony Anghie, Duncan Kennedy, Martti Koskenniemi and Anne Orford, and their critics. We will discuss core concepts such as sovereignty; just war; balance of power; accountability; individual rights and duties; but also examine how the history of colonialism helps us to understand what is currently happening in the sphere of 'Big Data' and to engage with TWAIL critique of international law (B.S. Chimni) in an indepth way. We will end this course with a discussion of the responsibility of the international lawyer today. This course combines both a lecturing and a seminar style of teaching. The course runs in the Spring Semester of 2021. Two to four hrs of teaching a week (tbc).