Complex interventions are needed to effectively tackle non-communicable diseases. However, complex interventions can contain a mix of effective and ineffective actions. Process evaluation (PE) in public health research is of great value as it could clarify the mechanisms and contextual factors associ­ated with variation in the outcomes, better identify effective components, and inform adaptation of the intervention. The aim of this paper is to demonstrate the value of PE through five case studies that span the research cycle. The interven­tions include using digital health, salt reduction strategies, use of fixed dose combinations, and task shifting. Insights of the methods used, and the implications of the PE findings to the project, were discussed. PE of complex interventions can refute or confirm the hypothesized mechanisms of action, thereby enabling intervention refinement, and identifying implementation strategies that can address local contextual needs, so as to improve service delivery and public health outcomes.