A war crime may be defined as a serious violation of a rule of international humanitarian law (IHL) which brings about individual criminal liability. To establish whether an act constitutes a war crime it is thus necessary to establish that IHL applied to and regulated the act. Hence, it must also be established that an international or non-international armed conflict existed at the time and place where the act occurred, and that the act had sufficient nexus to the armed conflict. The present article focuses on the classification of conflict and the nexus between the act and the conflict in Swedish legislation and case law in the light of international law.This article is part of a volume on investigation and prosecution in Scandinavia of international crimes.