There are a number of treaties of quasi-universal application that govern the conduct of belligerents in international armed conflict. Armed conflict is the trigger concept that gets the rules of international humanitarian law to operate and to override some of the peacetime rules of international law. This chapter tries to identify possible parameters with which to determine when the rules applicable in international armed conflicts apply, particularly whether they apply when only low intensity fighting has occurred. It examines legal texts, State practice and judicial decisions, as well as legal doctrines. The International Criminal Tribunal for the Former Yugoslavia (ICTY) looked into the definition of armed conflict more recently in The Prosecutor v. Tadic Case (Jurisdiction, Appeals) in 1995. The ICRC Commentary indicates that the Geneva Conventions are triggered regardless of the intensity or duration of fighting. Keywords:ICRC commentaries; ICTY decisions; international armed conflict