The paper explores the core elements of ‘due diligence’ as set out by Ruggie and highlights the similarities of the due diligence process to that of human rights impact assessment (HRIA). It argues that to implement the due diligence principle effectively, lessons must be learnt from previous experience of ‘institutionalising HRIAs’ as well as from analogous self-reflective regulatory processes. Such experience dictates that there are three essential elements, beyond those set out by Ruggie, that are pre-requisites of effective due diligence – requirements of transparency; external participation and verification; and monitoring and review. The required content of these elements is explored and recommendations made for minimum standards in relation to each element. The paper concludes that, without adherence to these standards, the human rights community and TNCs themselves should reject the principle of human rights due diligence as a pointless and self-defeating endeavour. [full paper can be downloaded]