Customary International
Humanitarian Law

THE study identifies 161 rules of customary international humanitarian law that strengthen the legal protection for victims of armed conflicts. It is the result of more than eight years of research and consultation. The study was undertaken at the request of the 26th International Conference of the Red Cross and Red Crescent in December 1995. In addition to treaty law, customary law is one of the main sources of international humanitarian law (IHL). In fact, until the codification of humanitarian law, which started in 1864 with the adoption of the first Geneva Convention, custom was the main source of humanitarian law for centuries. Whereas treaties are written conventions, customary international law derives from the practice of states and is unwritten. A rule is deemed customary, and as such binding on all states, if it is based on widespread, representative and virtually uniform practice supporting the rule.

The difficulty lies in the identification of customary international law and this explains why states sought the assistance of the ICRC in this identification process. This requires in-depth research into the practice of states which consists of an examination of military manuals, legislation, case-law and official statements from states throughout the world. This practice is catalogued by topic in the second, 4,000 page volume of the study. The research of practice and its assessment was carried out in consultation with experts from around the world. The rules that were found to be customary on the basis of this practice are set out in
Volume I.

Main findings

The purpose of the study was to overcome the limitations of treaty law which hamper the legal protection of victims of armed conflicts.

First, treaties only apply to states that have ratified them. While the four Geneva Conventions of 1949 have been universally ratified, other treaties such as the 1977 Additional Protocols to the Geneva Conventions have not, and as a result, are not binding on a number of states involved in armed conflict today. However, the study shows that many of the rules contained in such treaties are part of customary international law and, as such, apply to all states and to all parties to a conflict.

Second, even though non-international armed conflicts represent the majority of contemporary armed conflicts, treaty law does not regulate them in sufficient detail. Treaty law applicable to non-international armed conflict is limited to common article 3 of the four Geneva Conventions and the few articles of Additional Protocol II which contain only a very rudimentary regulation of the conduct of hostilities and humanitarian relief operations for example. The study shows, however, that state practice has developed a more complete regulation of internal conflicts under customary law than in treaty law. In fact, 149 out of the 161 rules identified in the study apply to non-international armed conflicts. The study thus clarifies the protection that is legally due to people affected by internal conflicts, such as those in Colombia, the Democratic Republic of the Congo, Nepal and Sudan. It is relevant in this respect to underline that in such internal conflicts, both governmental armed forces and rebel forces are bound by these customary rules and can be held accountable in case of non-compliance.

Third, in order to determine which treaty law applies to a particular conflict, a prior characterization of the conflict as international or non-international is required and this is often difficult or subject to dispute. The study shows, however, that many rules apply equally in international and non-international armed conflicts. For example, the prohibition of attacks on civilians, journalists or humanitarian relief personnel and the prohibition of forced displacement of populations apply in any armed conflict.

A user-friendly study

In order for customary law to have a practical impact on the ground it must be known and used not only by academics but by all those dealing with IHL. This includes military lawyers, government officials and national and international courts and tribunals that are required to enforce IHL. However, the study is user-friendly and easily accessible to non-lawyers as well, making the customary rules readily available and understandable to anyone involved in situations of armed conflict, first and foremost the commanders and soldiers in the field, but also diplomats, journalists and humanitarian actors in general. The ICRC intends to make full use of this study in its work to protect and assist victims of armed conflict. It will draw on the study to remind parties to a conflict of their obligations. In order to promote the study the ICRC is organizing a series of launch events around the world in 2005 and 2006.

Initial feedback

Robert Kolb
Professor of international law at Neuchâtel, Bern and Geneva Universities.
“What is the relevance of custom with respect to treaty law? It can be useful in several ways. First, it can serve to interpret treaty law: practice shows how a norm is understood leading to a common interpretation. Such practice can also take the form of jurisprudence (for example the rulings of the International Criminal Tribunal for the Former Yugoslavia). Second, custom fills the gaps created because certain states are not party to important instruments (for example, the United States has not ratified the 1977 Additional Protocol I). Third, custom is a valuable vehicle for the development of the law pertaining to non-international armed conflicts, which are not yet regulated in sufficient detail. Lastly, custom provides a common yardstick in certain situations, such as when contingents of different nationalities are engaged in a joint operation and their governments have not ratified the same instruments (for example, in Somalia in 1992). The multiplicity of applicable rules can thus to a certain extent be overcome.”

Judge Theodore Meron
President, International Criminal Tribunal for the Former Yugoslavia.
“What makes the study unique is the seriousness and breadth of method for the identification of practice, with national studies of nearly 50 countries. While it is probable that the study will be challenged in some cases, especially as regards the formulation of the black letter rules, there is no question that any future discussion of customary law will have the study as its starting point. It may well be that in some cases, it will be the description of practice described in the study that will be drawn on by states and by courts, rather than the black letter rule.”

Yves Sandoz
ICRC member and lecturer at Geneva and Fribourg universities.
“This undertaking has particular significance at a time of renewed tension for humanity when religious and cultural frictions are being exploited for violent ends. The Geneva Conventions have been universally embraced. The rules of international humanitarian law represent a kind of common heritage of mankind, with its roots in all human cultures. They can therefore be viewed as a cement between different cultures. It is thus essential to remind people of those rules and persuade them to comply. The study has been a golden opportunity to do this. The study is a still photograph of reality, taken with great concern for absolute honesty, that is, without trying to make the law say what one wishes it would say. I am convinced that this is what lends the study international credibility. But though it represents the truest possible reflection of reality, the study makes no claim to be the final word. It is not all-encompassing — choices had to be made — and no one is infallible… May it be read, discussed and commented on. May it prompt renewed examination of international humanitarian law and of the means of bringing about greater compliance and of developing the law.”