It refers to the use of force to repel an attack or imminent threat of attack directed against oneself or others or a legally protected interest.
Self-defense in international law refers to the inherent right of a State to use of force in response to an armed attack. Self-defense is one of the exceptions to the prohibition against use of force under article 2(4) of the UN Charter and customary international law. However, whether the armed attack that gives rise to self-defence should originate from another state (as opposed to an armed group) and whether the attack should actually materialize to lawfully invoke self-defense are ongoing conundrums for scholars.
The concept of self-defence and defence of others is also used in criminal law as a defence to justify a necessary and proportionate use of force against an unlawful attack. Such conduct by civilians does not constitute direct participation in hostilities.
See Ius ad bellum;
UN Charter, Chapter VII
UN Charter, Art. 51
International Law Commission, Articles on State Responsibility (Part A., Arts 21, 26 and Para. 3 of the commentary of Art. 21)
ICJ/Israel, Separation Wall/Security Fence in the Occupied Palestinian Territory (Part A., Paras. 138-139)
ICTY, The Prosecutor v. Martic (Part C., Para. 268)
ICTY, The Prosecutor v. Kupreskic et al. (Paras. 511-520)
in criminal law
The International Criminal Court (Part A., Art. 31(1)(c))
International Law Commission, Articles on State Responsibility (Part A., Para. 3 of the commentary of Art. 21)
CASSESE Antonio, “Under What Conditions May Belligerents Be Acquitted of the Crime of Attacking an Ambulance?”, in Journal of International Criminal Justice, Vol. 6, No. 2, 2008, pp. 385-397.
DINSTEIN Yoram, War, Aggression and Self-defence, 3rd edition, Cambridge, CUP, 2001, 318 pp.
GALAND Renaud & DELOOZ François, “L’article 31, par. 1 c) du Statut de la Cour pénale internationale : une remise en cause des acquis du droit international humanitaire?”, in IRRC, No. 842, June 2001, pp. 533-538.