This Chaillot Paper examines burdensharing patterns between the United States and Europe, focusing in particular on the time period since the 9/11 attacks. It does so by analysing military and civilian burdensharing activities undertaken to address the high-priority challenges identified in the 2002 US National Security Strategy (NSS) and the 2003 European Security Strategy (ESS). Among the principal categories considered are burdensharing activities to enhance regional stability, to fight terrorism, to counter the proliferation of weapons of mass destruction, and limit the potential for state failure. This paper should be of interest to a wide audience, especially those interested in the evolution of US-European relations in the security field. In particular, it should appeal to analysts and academics on both sides of the Atlantic monitoring burdensharing patterns and the collaborative measures taken to address present-day security challenges.