Abstract
<jats:title>Abstract</jats:title> <jats:p>Due diligence has long been understood as both a duty and a constraint upon State behaviour. Can it perform the same role in relation to investor conduct? The principal aim of this article is to provide a novel and systematic analysis of investor due diligence in international investment law. It problematizes the emerging approaches to investor due diligence by situating it at the heart of the competing visions on how international investment law articulates fairness through the standards of appropriate behaviour for States and investors, respectively. The article interrogates how arbitral approaches to due diligence expose international investment law’s enduring asymmetries, deficits, and resistance to change, especially when it comes to incentivizing and enforcing responsible and accountable investor conduct.</jats:p>