This chapter critically discusses the proceduralisation of due diligence obligations. The chapter defines proceduralisation as a process gradually eroding the ‘reasonable’ standard traditionally linked to due diligence and substituting it with specific legal parameters. Through proceduralisation, the content of due diligence obligations is ‘spelled out’ into a series of sub-duties, tecnical standards and direct obligations (including procedural ones) whose fulfilment is required for assessing compliance with the standard of due diligece of the ‘principal’ obligation. The first part of this chapter critically explores this phenomenon, arguing that proceduralisation through interpretative practice raises challenges and comes close to creating new legal rules. The second part illustrates proceduralisation through two case studies taken from international environmental protection and due diligence obligations in international human rights law. The chapter argues that the proceduralisation of due diligence obligations fundamentally tests their dogmatic structure by affecting their nature and content.