Most existing analyses of counterterrorism cooperation among EU Member States (MSs) have focused on the formal EU agencies and institutions, which may be regarded as direct vertical extensions of political and executive power in the EU MSs. When it comes to practical cooperation, however, it appears that national security, judicial and intelligence agencies in Europe often prefer the utilize several horizontal non-EU counterterrorism arrangements that comprise a differentiated set of members in the form of a more networked, enhanced co-operation. Because of their flexibility, relative independence from national governments, as well as their ability to include a broad range of participants on equal footing, it is generally assumed that these informal policy networks are more suitable for tackling governance problems or achieving common goals than their more formal and hierarchical EU counterpart. In this paper, however, I argue that even these informal multilateral arrangements suffer from a number of weaknesses and shortcomings and thus may not always be preferable avenues for counterterrorism cooperation among EU MSs.