Irregular warfare is a fundamentally European concept that arose in the 18^th century to refer to the reverse of a set of practices and representations established as norms for armed conflict. Whether consciously or not, irregular combatants defy modern western military categories, in tactical and strategic terms, as well as in political and legal ones. In its various forms, irregular warfare has resulted not only in guerrilla warfare campaigns against occupying armies but also in clandestine or subversive actions aimed at surprising or circumventing a more powerful foe by attacking it logistically or politically behind the lines. With the reduction in the classical battle model immediately after World War II, irregular warfare has gradually imposed itself as the dominant mode of conflictuality, through both guerrilla warfare and terrorism. This prevalence is the result both of indirect confrontations between major powers and of asymmetrical conflicts following decolonization.