This book asks why European countries tried to build a security institution outside of NATO, emphasising the influence of political party ideologies.Despite NATO's success in managing European security policy, European governments have repeatedly tried to build a new security institution in NATO's shadow. This book reflects on how national parties' ideologies motivate governments to attempt to create these institutions and affect the rate of success when they do so.Despite NATO's success in managing European security policy, European governments have repeatedly tried to build a new security institution in NATO's shadow. This book reflects on how national parties' ideologies motivate governments to attempt to create these institutions and affect the rate of success when they do so.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.1. Introduction; 2. Political party ideology and security cooperation; 3. The success and failure of European security cooperation; 4. The end of the Cold War and the Maastrichtl3l