International law is playing an increasingly important role in international politics. However, international relations theorists have thus far failed to conceptualise adequately the role that law plays in politics. Instead, IR theorists have tended to operate with a limited conception of law. An understanding of jurisprudence and legal methodology is a crucial step towards achieving a better account of international law in IR theory. But many of the flaws in IR's idea of law stem also from the theoretical foundations of constructivism – the school of thought which engages most frequently with law. Adriana Sinclair rehabilitates IR theory's understanding of law, using cases studies from American, English and international law to critically examine contemporary constructivist approaches to IR and show how a gap in their understanding of law has led to inadequate theorisation.