One need only consider for a moment the vast array of terrorist groups and their ideologies to grasp the diversity of motivations, tactics, and damage wrought by terrorists around the world. In spite of these differences, scholars have begun to compare and contrast terrorist groups in different polities, arguing that we can learn lessons from such comparisons – especially in transferring counter-terrorism policies from one context to the next. Recent studies on terrorism have provided new ways to compare terrorist groups across cases. Analyses of terrorist groups and incidents have begun to recognize the evolutionary nature of terrorism, as well as its ability to adapt to counter-terrorism tactics. Moreover, scholars have noticed that terrorist tactics tend to be “contagious” in that some terrorist groups either emulate other groups’ successes or learn from their mistakes.