Terrorist designation has increasingly become an important counterterrorism tool used by intergovernmental organizations and state governments. This article examines the determinants of terrorist listing and argues that terrorist listing is driven by security as well as political concerns. While countries tend to designate groups that pose a greater security threat, terrorist listing can also be influenced by interstate relationships including alliance ties and state rivalry. We test these arguments using a dataset on 35 countries that currently maintain their own lists of designated terrorist organizations. Our findings show that governments are more likely to list groups that have a record of attacking their domestic interests. Domestic groups are more likely to be designated than foreign groups. Moreover, countries are more likely to designate groups that are designated by their allies, even when these groups do not pose a direct threat. Our study contributes to the literature on terrorism and more broadly international security by systematically examining the determinants of terrorist designation and explaining the heterogeneity of terrorist lists across countries.