Due Diligence

In international law and policy practice, due diligence is an obligation of conduct rather than result: an actor must take reasonable, good-faith steps to prevent, investigate, or mitigate harm, even if it cannot guarantee a particular outcome. The standard appears across multiple regimes, including transboundary environmental harm, human rights, cybersecurity, and corporate responsibility.

The principle is often traced to the Trail Smelter arbitration (US v. Canada, 1938/1941) and the ICJ's Corfu Channel case (1949), which held that every state has an obligation "not to allow knowingly its territory to be used for acts contrary to the rights of other States." The International Law Commission's 2001 Draft Articles on Prevention of Transboundary Harm from Hazardous Activities articulate due diligence as the core preventive duty for environmental risks.

In the human rights field, the UN Guiding Principles on Business and Human Rights (endorsed by the Human Rights Council in 2011) require companies to conduct human rights due diligence — identifying, preventing, and accounting for adverse impacts in their operations and supply chains. The OECD Guidelines for Multinational Enterprises incorporate a similar framework. National laws now codify these expectations, including France's Loi de Vigilance (2017), Germany's Lieferkettensorgfaltspflichtengesetz (2021), and the EU's Corporate Sustainability Due Diligence Directive (CSDDD, adopted 2024).

In professional practice, due diligence also refers to:

• Legal/financial DD before mergers, acquisitions, or investments — reviewing contracts, liabilities, and compliance.
• Sanctions and AML DD — know-your-customer checks under FATF recommendations.
• Research DD — verifying sources, dates, and authenticity before citing or publishing.

What unifies these uses is a reasonableness threshold calibrated to the actor's size, capacity, and the severity of potential harm. Failure to meet it can trigger state responsibility, civil liability, or reputational consequences, even where the underlying harm was caused by a third party.