The principle of proportionality is a basic principle of International Humanitarian Law (IHL), meant to limit the damages caused by military operations on civilian population and objects. It demands that minimal harm is caused to civilians in a conflict, and when harm to civilians must occur, it needs to be proportional to the military advantage. This principle is codified in Article 51(5)(b) of the Additional Protocol I. It is also mentioned in the Additional Protocol II and in the Amended Protocol II to the Convention on Certain Conventional Weapons. A large number of military manuals like Sweden’s IHL Manual also talks about the principle of proportionality. Apart from these, many States have enacted legislations making any attack not conforming with the principle of proportionality an offence.

The principle finds applicability in all the cases where the civilians find themselves vulnerable to the attacks even when they are not taking a direct part in the hostilities. No exceptions can be created through the means of this principle, neither can it be used to override specific protections where the text does not provide for the same.

In the sphere of international law, States do not have an authorization to use armed force unless it is for the purpose of self- defence or aggression. Only proportional force is allowed to respond. This fact was reiterated in the case of Nicaragua v. United States of America, where the International Court of Justice opined that “self-defence […] warrant[s] only measures which are proportional to the armed attack and necessary to respond to it, a rule well established in customary international law”.

In Public Committee against Torture in Israel v. the Government of Israel, the Israeli apex court recognized that the principle of proportionality is not only a general principle of international law but also one of the core principles of humanitarian law in general, especially in situations of military occupation.

In 2004, in Physicians for Human Rights v. Commander of IDF Forces in the West Bank, it was examined whether the intervention of the Israeli armed forces in Rafah (Gaza Strip) was legal. In the very case, the Apex court of Israel recognized that the argument of “necessity” can play an important role in the justification of a military operation. It further observed that even though a non-proportional military operation can be legitimate from a military point of view, it would still be unlawful.

In a world where the people cannot afford any more losses due to armed conflicts, the principle of proportionality acts like a boon. The test ensures that no attack upon innocent civilians shall be permitted if the collateral damage caused to them is not proportional to the military advantage (in protecting combatants and civilians). Thus, this core principle of IHL is a principle that cannot be neglected by any State or non-State actors participating in a conflict.