This chapter analyses how an international wrongful act accrues from the violation of a due diligence obligation and its consequences. The first part discusses due diligence obligations against secondary rules of ARSIWA concerning the existence of a wrongful act. It is argued that violations of due diligence obligations stem from omissions and that the difficulty of establishing responsibility for failure of due diligence typically concerns the application of rules governing the breach, rather than rules of attribution of conduct. Accordingly, a critical reappraisal of the genealogy of Article 14(3) of ARSIWA and breaches of preventive obligations is undertaken; the chapter argues that the ILC wrongly conceptualised the ‘event’ to be prevented as a secondary rule, this way confusing the relationship between prevention and due diligence. The rest of the chapter examines due diligence obligations against other relevant secondary rules, such as circumstances precluding wrongfulness (specifically, force majeure and distress), the relationship between due diligence and complicity, and how reparation is to be accorded following a breach of due diligence obligations.