Due Diligence

The concept of due diligence, though long acknowledged in legal doctrine, gained practical significance through arbitral jurisprudence in the late nineteenth and early twentieth centuries, in cases concerning neutrality law and the treatment of foreign nationals. In these early decisions, due diligence was invoked to assess states’ obligations to prevent and punish harmful acts committed by private individuals against other states, their nationals, or their property. Over time, the notion of due diligence expanded beyond this initial framework, taking root in various branches of international law, including environmental law, the law of the sea, human rights law, international humanitarian law, investment law, and diplomatic law. As its scope widened, its nature evolved and became more complex. A growing doctrinal consensus now defines due diligence as a standard of conduct attached to specific legal obligations—so-called obligations of conduct. However, the term is also used to describe obligations of vigilance—that is, duties to prevent the use of a state’s territory in ways that may cause harm to the territory, property, or persons of another state—or, more broadly, to refer to a general principle of law embodying a duty of care aimed at preventing transboundary harm. Moreover, although due diligence was originally conceived within the framework of state responsibility, the range of its duty-bearers has diversified. Today, not only states but also international organizations, corporations, non-governmental entities, and even individuals may be subject to due diligence obligations, thereby blurring its conceptual contours and contributing to its doctrinal complexity. The word “diligence” derives from the Latin diligentia, meaning scrupulous care, attention, or accuracy. As such, due diligence obligations require to act reasonably or to adopt reasonable measures. While this standard affords a certain margin of discretion, it does not permit unfettered freedom of action. The specific measures required vary according to the factual and legal context, including the actor’s capacity to act, the applicable branch of international law, and relevant normative frameworks—such as prevailing ethical standards, industry practices, or commercial customs. The principal domain of due diligence lies in the prevention of risk—whether arising from private actors, natural events, or technical and industrial activities. A failure to take appropriate preventive measures may result in international responsibility, even if the harmful acts themselves are not directly attributable to the state. In this way, due diligence helps bridge the so-called “liability gap” in international law, thereby reinforcing accountability mechanisms in a global order increasingly shaped by interdependence, privatization, and rapid technological change.