Kosovo has raised three international debates. Firstly, NATO’s decision in March 1999 to go to war over Kosovo created a deep division within the United Nations. The second debate was about the creation of an international administration for Kosovo and the third is now about the future status of the territory. The six ‘just war’ principles – a just cause, last resort, likelihood of success, proportionality, right intentions and legitimate authority – are traditionally applied to war settings in order to assess the legitimacy of the use of force. They can be also used to answer the question to what extent the Kosovo conflict set a political model for forceful external involvement in a secessionist crisis with severe humanitarian consequences. But these six jus ad bellum principles can also be of heuristic value for dealing with the legitimacy of the creation of an international administration in Kosovo, and with Kosovo’s right to unilateral secession and its recognition by other states.