Debates about the role and relevance of international law in contemporary world have acquired new intensity in light of the US-UK coalition's decision to invade Iraq in March 2003 without a clear legal basis. Some have interpreted the lack of compliance in this case as proof of irrelevance of the UN Charter use of force paradigm, while others have understood the use of legal arguments in this event as confirming the validity and weight of international law on the use of force. Motivated by these debates, this paper takes a deeper look at how international law on the use of force operates in the broader context of international politics and in what ways it may affect political processes and outcomes in this highly sensitive area. Integrating and building on different perspectives of both IL and IR scholarship, the first part of the paper explores two such important pathways through which international law may affect the political processes with respect to the use of force: firstly, as a regulatory framework, providing a set of legal parameters delimiting the range of acceptable policy choices; and secondly, as a relatively autonomous, objective and authoritative source and measure of legitimacy of political action. Applying the theoretical propositions developed in the first part, the second part then examines the role of international law in the processes of shaping, justifying and evaluating the decision of the US-UK coalition to use force against Iraq. Eventually, this ultimate test-case confirms that international law on the use of force plays a significant role in contemporary international politics, albeit not always in the sense in which it has been traditionally explained or expected