This article examines the international legal framework applicable to intelligence sharing in multinational military operations, with a particular focus on complicity scenarios. It first provides a theoretical overview of the role of fault in complicity, of how intent and knowledge can be conceptualized, and of the attribution of fault to States. It then looks in detail at the rule codified in Article 16 of the International Law Commission’s Articles on State Responsibility, and argues that this rule is best understood as employing multiple modes of fault (direct and indirect intent and wilful blindness). The article also argues that international humanitarian law (IHL) and international human rights law (IHRL) possess their own complicity rules. These regime-specific rules can apply to State assistance to non-state actors and can employ more relaxed modes of fault than Article 16. A State could thus be responsible for facilitating the commission of serious violations of IHL and IHRL through the sharing of intelligence or the provision of other aid if it consciously disregarded a risk that its partner would commit such violations with the aid provided. The article then looks at the role that mitigation measures employed by the assisting State, such as diplomatic assurances, have in assessing its responsibility for complicity, and at whether risks generated by the provision of assistance can lawfully be balanced against the risks generated by suspending assistance. Finally, the article examines two basic scenarios – that of sharing intelligence that facilitates a partner’s wrongful act, and that of receiving unlawfully obtained or shared intelligence.