The relationship between Islam and international law has long been studied, primarily in the field of the law of war and international humanitarian law (Humanitarian Law, International). Particularly in the past two decades, this relationship has been expanded to some other international law areas including human rights and international terrorism. The main reason for this increased attention to the relevance of Islam for international law is States’ and non-State actors’ repeated references to Islamic legal rules for explaining or justifying a certain position in their relations with other international law actors. The relevance of Islam to international law should be assessed with due regard to substantive legal principles and rules that Islam contains. A prerequisite for an objective assessment is to contextualize them through a glimpse into the Islamic conception of international law, the sources of Islamic international law, and the legal history of this law.