The main aim of aim this study is to analyse the challenges faced by the United Nations in its involvement in countries that have been targeted by foreign military interventions that have not been authorised by the Security Council of the United Nations. The study does not examine the patterns of reaction to military intervention as such. Instead, the focus is on the United Nations’ response to the outcome of the military interventions at two main levels. The first is at the level of the Security Council and the decisions taken there on the nature and scope of the involvement of the United Nations in the post-intervention developments in the target state. The second level is the level of the target state and the challenges that the United Nations may face in carrying a given mission. A core dimension addressed in the study is how the United Nations’ responds to demands that it involves itself in situation resulting from actions that it had not authorised beforehand. Another dimension is the question of the legitimacy of the United Nations on the ground in the target state of the intervention. The later is of particular relevance when there is armed resistance to the intervening forces.