["Criminology & Public Policy, Volume 20, Issue 1, Page 177-203, February 2021. ", "\n\nResearch Summary\nThis study offers an empirical insight into terrorists’ use of the Internet. Although criminology has previously been quiet on this topic, behavior‐based studies can aid in understanding the interactions between terrorists and their environments. Using a database of 231 US‐based Islamic State terrorists, four important findings are offered: (1) This cohort utilized the Internet heavily for the purposes of both networking with co‐ideologues and learning about their intended activity. (2) There is little reason to believe that these online interactions are replacing offline ones, as has previously been suggested. Rather, terrorists tend to operate in both domains. (3) Online activity seems to be similar across the sample, regardless of the number of co‐offenders or the sophistication of attack. (4) There is reason to believe that using the Internet may be an impediment to terrorists’ success.\n\n\nPolicy Implications\nThe findings of this study have two important policy implications. First, it is vital to understand the multiplicity of environments in which terrorists inhabit. Policy makers have tended to emphasize the online domain as particularly dangerous and ripe for exploitation. While this is understandable from one perspective, simplistic and monocausal explanations for radicalization must be avoided. Terrorists operate in both the online and offline domain and there is little reason to believe that the former is replacing the latter. The two may offer different criminogenic inducements to would‐be terrorists, and at times they may be inseparably intertwined. Second, when policy responses do focus on online interventions, it is vital to understand the unintended consequences. This is particularly the case for content removal, which may inadvertently be aiding terrorists and hampering law enforcement investigations.\n\n"]