International Humanitarian Law


International humanitarian law (IHL), also known as the laws of war or the law of armed conflict, is the legal framework applicable to situations of armed conflict and occupation. As a set of rules and principles it aims, for humanitarian reasons, to limit the effects of armed conflict.

Fundamental to IHL are the following two principles:

  1. Persons who are not, or are no longer, participating in hostilities must be protected; and
  2. The right of parties to an armed conflict to choose methods and means of warfare is not unlimited.

IHL is a part of public international law.  Public international law is a broad set of treaties, customary law, principles and norms.  The framework traditionally regulated relationships only between States. It has evolved, however, to cover a broad range of actors. IHL is notable in this regard, as it recognizes obligations for both States and non-State armed groups that are parties to an armed conflict.

IHL regulates activity during armed conflict and situations of occupation. It is distinct from, and applies irrespective of, the body of law that regulates the recourse to armed force. This framework is known as the jus ad bellum, and is enshrined in the UN Charter. It regulates the conditions under which force may be used, namely in self-defense and pursuant to UN Security Council authorization. Once there is an armed conflict IHL applies to all the parties, whether or not a party was legally justified in using force under jus ad bellum principles.

At its core IHL represents a balance between military necessity and humanitarian considerations in the context of conflict.  Humanity, as a cornerstone of IHL, represents the imperative during conflict to alleviate suffering and save lives, and to treat humanely and respectfully each individual. Military necessity is the justification of measures necessary to achieve a military goal, provided these measures comply with international humanitarian law.

The balancing of humanity and military necessity is seen in the foundational IHL norms of distinction and proportionality. Parties to an armed conflict are required to distinguish, at all times, between civilians and combatants and between civilian objects and military objects. Additionally, an attack may not be launched if it is anticipated to cause incidental loss of civilian life, injury to civilians, or damage to civilian objects that would be excessive in relation to the direct military advantage anticipated. Additional IHL principles include the duty to take precautions to spare the civilian population before and during an attack, the prohibition against infliction of unnecessary suffering or superfluous injury, and the prohibition of indiscriminate attacks.

Classification of Armed Conflict

IHL classifies armed conflicts as either international armed conflict (IAC) or non-international armed conflict (NIAC). The proper categorization of an armed conflict is necessary to determine which set of rules apply to the conflict: those for an IAC (found mainly in the four Geneva Conventions and Additional Protocol I) or those for a NIAC (found mainly in Article Three common to the four Geneva Conventions and Additional Protocol II). Situations of occupation are regulated by IHL, namely the Fourth Geneva Convention and Additional Protocol I.

Whether or not an armed conflict is an IAC or a NIAC has significant implications. For instance, prisoner of war (POW) status, as well as combatant status, is found only in the rules applicable to IACs. The rules regulating the conduct of hostilities, as well as humanitarian access and assistance, are more detailed for IACs. All together the treaty rules applicable to IACs total close to 600; those applicable to NIACs number less than 30. This dearth of guidance can pose a challenge because the majority of contemporary conflicts are NIACs. To address this, one can look to customary international law, which includes a number of rules that have evolved to address both IAC and NIAC situations.

The definition of an IAC is found in Article Two common to the four Geneva Conventions. It states that the rules of IAC apply to “all cases of declared war or of any other armed conflict which may arise between two or more of the High Contracting Parties . . . .“ Thus, an IAC can only be between two or more States.

In Article Three common to the four Geneva Conventions a NIAC is defined in the negative, as “an armed conflict not of an international character.” Thus, if a non-State armed group is a party to the armed conflict, it will be categorized as a NIAC. This could be the case if, for instance, a State is fighting an armed group, or if two non-State armed groups are fighting each other. Common Article Three and customary international law would regulate both scenarios. For Additional Protocol II to apply, certain requirements must be satisfied. In the armed conflict, a State must be on one side, fighting against an armed group. That State must have signed Additional Protocol II for it to apply. Additionally, the non-State armed group must be organized, under a responsible command, and exercising control over part of the territory in such a manner that the group is able to carry out military operations.

The use of the phrase “global war on terror” resulted in some misunderstanding regarding the application of IHL to certain situations. The “global war on terror” is a political phrase, not a legal term of art. Thus, the “global war on terror” is not an armed conflict. The appropriate way to analyze conflicts that fall under this umbrella is to look at the conflict locations – Iraq, Afghanistan, Somalia, Yemen, etc. – and assess each one in terms of whether or not it is an IAC or a NIAC, regulated by the relevant framework.

There is some academic debate regarding cross-border NIACs, as well as at what point a NIAC might become an IAC, or an IAC might become a NIAC. These analyses are context and fact-dependent. Despite the theoretical debate, practitioners can often work around them by relying on customary international law to argue for protections owed to civilians.


Treaties and customary international law are the two main sources of IHL rules and regulations. Treaties are agreements between States, and those States that ratify a treaty are bound by its terms. Though a non-State armed group cannot sign a treaty, IHL treaty rules like Common Article Three and Additional Protocol II nonetheless apply to these actors.

Many IHL rules are now considered to reflect customary international law as well. Customary international law consists of rules derived from the consistent practice of States based on a belief that the law requires them to act in that way. Such rules are binding on both states and non-State armed groups. The International Committee of the Red Cross published a study and created a database on customary international humanitarian law.

The key IHL treaties include the 1907 Hague Regulations, the four Geneva Conventions, and their Additional Protocols.


The International Committee of the Red Cross has an International Humanitarian Law page that provides a number of introductory IHL resources.

The Geneva Academy of International Humanitarian Law and Human Rights hosts the Rule of Law in Armed Conflicts Project that provides a database of relevant legal instruments and overviews of current IHL issues.

The International Committee of the Red Cross hosts an IHL treaty database on its website.