The present paper explains the meaning, origin, source and evolution of Muslim international law (Siyar). It further attempts to locate the role and place Muslim International law. It also concludes that since Islamic law is not only one of the principle legal systems in the world but also that Islam is one of the main forms of civilizations; therefore, Islamic law must be one of the sources of International law. Siyar (Muslim international law) only strengthens the obligations of Muslim states and does not impose Islamic law on non-Muslim states. It also discusses the some modern scholar’s definitions of Muslim international law.