Today, international law is everywhere. Wars are declared and conducted in its name, and in its name rights are both protected and renounced. It is also international law which determines who owns and uses the world's scarcest resources. Thus, international law is part of a dangerous and unjust world - a part of how we are governed globally. But, it can also be used to challenge aspects of this world and to give voice to projects which seek to transform the institutions of global governance. In this collection of essays, Professor Martti Koskenniemi - a well known practitioner and one of the great theorists and historians of international law - examines the recent debates on humanitarian intervention, collective security, protection of human rights, and the 'fight against impunity.' Additionally, Koskenniemi reflects on the use of the professional techniques of international law to intervene politically. The essays both illustrate and expand his influential theory of the critical role of international law in international politics.