What factors drive cooperation in the counterterrorism (CT) domain? Although in the last twenty years, many scholars have been studying terrorism and CT, such a question has remained unanswered so far. Very few attempts have been made, hence new researches are needed.

The here-present paper addresses this issue, providing a twofold contribution. First, it fosters existent analyses by proposing a new theoretical framework that combines CT studies and alliances literature. Both fields have underlined different aspects, however, none of them has been able to give a satisfactory answer. By merging their most decisive insights, it is instead possible to reach a more complete and exhaustive response. This explanation considers citizens’ role, states’ domestic structures, alongside the impact of terrorism as well as the organization of CT departments.

Second, the theoretical framework is then tested on a newly collected dataset using panel data analysis. This original dataset comprehends CT bilateral agreements signed by European countries between 2002 and 2017. Treaties have been taken from OSCE reports, UN Treaty Series, and Lexis Nexis.

The results illustrate two important aspects. First, domestic features do matter: governments’ composition and citizens’ threat perception are pivotal factors, next to other conditions such as states’ geographical position. On the other hand, the findings show how citizens’ perception of terrorists’ threat is much more important for cooperation than the actual impact of terrorism.