Article 16 of the International Law Commission's Articles on State Responsibility provides that a State that aids or assists another State in the commission of an internationally wrongful act by the recipient State is internationally responsible, where certain conditions are fulfilled. This article clarifies one of those conditions, namely the difficult and contested issue of what degree of knowledge or intent engages the responsibility of an assisting State under Article 16. The article focuses particularly on assistance in armed conflict and counterterrorism situations, which increasingly feature some form of operational or intelligence cooperation between States.