NATO has been a successful forum for managing European security policy. Yet European governments have repeatedly tried to build a new security institution in NATO's shadow. In this innovative book, Stephanie C. Hofmann asks why governments attempted to create an additional institution despite no obvious functional necessity and why some attempts failed while others succeeded. European Security in NATO's Shadow considers security cooperation through the lens of party ideologies to shed new light on these questions. She observes that political parties are motivated to propose new institutions by their multidimensional ideologies. Moreover, the success of efforts to create such institutions depends on the degree of ideological congruence among parties in power. In particular, the relationship between the values of multilateralism, sovereignty and Europe informed the impetus and success rate of the attempts made during negotiations for the Maastricht, Amsterdam and Nice treaties to create a European security institution.