Abstract
Proscription lists are common counter-terror tools, yet their impact on terrorist violence is unclear. We find that proscription can be effective at constraining the violence of some types of groups, especially those that are young, secular, and without institutional support. However, proscription also can backfire from a counter-terrorist prospective, especially when applied to groups that are well-established, religious, and/or sponsored by states. Our analysis evaluates 534 terrorist groups, including sixty-six that were ultimately proscribed under the United States’ Foreign Terror Organization list. Unsurprisingly, we find that terrorist groups that attract proscription are more violent and better equipped to tap into international terror networks. While younger groups and nationalist groups are more vulnerable to proscription, older religious groups and those with state sponsors seem to be more violent after proscription. Proscription can be an effective tool for reducing terrorist attacks and lethality, but it is most effective against younger terror groups and states should exercise caution in its use as it may not have the desired effects on all types of groups.