International Law in Islam: An Analysis of Its Theoretical Construction and Application in the Diplomacy of Muslim Countries

International law plays an important role in maintaining stability in interstate relations, including in the Islamic context which emphasises principles such as ukhuwah Islamiyah and the caliphate. This research aims to investigate the role of international law in Islam and its impact on the diplomacy of Muslim countries. The method used is a literature study with a qualitative-descriptive approach, which includes the analysis of various sources such as books, journals, and international documents. The results show that in Islam, international legal theory is based on sources such as the Qur’an, Hadith, Ijma’, Qiyas, Istihsan, and Maslahah Mursalah, with basic principles such as justice, equality, and state sovereignty. The concept of Islamic interstate relations includes dar al-Islam, dar al-Harb, and the laws of war and peace. While there are challenges in the application of Islamic international law, such as differences in interpretation and political dynamics, there are positive prospects for the future, including increased cooperation between states and advances in communication technology.