This contribution discusses the Gulf War of 1991-1991. It sets out the facts and context of the Iraqi invasion of Kuwait in August 1990, followed by the adoption of United Nation Security Council Resolution 678 (1990) and the subsequent military reaction by the United States-led international coalition. It assesses the reaction of the main protagonists and that of the broader international community to these events. In doing so, it also assesses the legal basis of the military response by the international coalition of the ‘willing and able’ against Iraq. It determines whether it was based on Article 42 of the United Nations Charter, or collective self-defence in terms of Article 51 of the United Nations Charter. The final section examines if and to what extent this case has had an impact on (the legal basis) of military measures taken in the interest of collective security in the post-Cold War era.