The introductory chapter, after providing an overview of the main themes and arguments, discusses the research gap. It shows that three types of writings have shortcomings. These focus, respectively, on soldiers and unconventional problems, explanations of military conduct, and the protection of civilians in military missions. This book fills a gap by comparing and explaining military responses to crime and insurgency in war-torn countries on the micro-level, and by analyzing local effects. Focusing on the concept of organizational routines, it puts military organizations at center stage, thus contributing to mid-level theories stressing domestic-level drivers of foreign policy. While all Western militaries struggle to achieve operational and tactical flexibility, military conduct in multinational missions varies, due to variations in organizational routines. Thus, some troops are better at coping with irregular adversaries than others. The introduction presents a causal mechanism that links governmental decisions to send soldiers abroad, routine military behavior triggered by deployment decisions, and the impact of military action on local populations. Subsequently, the chapter defines important terms and then discusses methodological issues: the selection of cases, the design, indicators, sources, and caveats regarding causality. In a final step, it presents the plan of the book.