International custom is considered one of the main important sources of public international law in general, and it is distinguished by its evolving nature and its ability to adapt to the changing conditions of international life. As well as its value and its past and present impact on the prevailing relations between the persons of international law. Furthermore, the custom in international human law has special importance to form the obligatory nature of its provisions and obligate all countries to it, even those that did not sign any convention that is related to the law. It also has the ability to limit the reservation to Conventions of International Humanitarian Law, and their amendments, which requires shedding light on this source, which is the most important among all other sources, regardless of the rank or position it occupies.

Keywords: Custom, International Humanitarian Law, Sources of International Humanitarian Law, Reservation to Treaties, Amending Treaties.