When pragmatic clinical trials are embedded in healthcare systems (ePCT), even when an intervention itself is relatively simple, the actual delivery of the intervention may be complex due to factors such as new workflows, special training of frontline staff, and the number of components in an intervention. Further adding to this complexity is that the intervention itself may be need to be to be delivered in multiple health systems and different types of clinicians may be involved with delivering the intervention (George et al. 2020). Thus, intervention delivery (i.e., accompanying procedures and activities) can be complex, and adequately planning for how to address these complexities is a vital component of any ePCT.

This chapter reviews what makes an intervention’s delivery complex, frameworks and guidance for studying complex interventions, and a tool for assessing the complexity of intervention delivery.