This paper analyses peacekeeping impartiality, i.e. the extent to which peacekeepers act in the interests of international peace and security, rather than the interests of specific states or other external actors. It reevaluates the question of impartiality through an analysis of the Congo operation of July–September 1960. This case study was selected because it was by far the most important instance of peacekeeping during the Cold War. Based upon primary source materials from US, British, and UN archives, as well as memoirs and secondary sources, it finds that the Congo peacekeeping force intervened to a considerable extent in the internal politics of the Congo; in doing so, the peacekeepers collaborated with US policymakers and, to some extent, advanced their strategic objectives. A comparison between the Congo operation and recent cases of peacekeeping in post-Cold War Africa indicates that impartiality is likely to remain an elusive goal.