Background: The ‘SCale-Up of diaBetes and hYpertension care’ (SCUBY) project aims to support the scale-up of integrated care for diabetes and hypertension in Cambodia, Slovenia, and Belgium through the co-creation, implementation, and evaluation of contextualized roadmaps. These roadmaps offer avenues for action and are built on evidence as well as stakeholder engagement in policy dialogues. These two implementation strategies – roadmaps and policy dialogues – are very much intertwined and considered to be key elements for successful stakeholder supported scale-up. Yet, little is known about how, why, and under which conditions a roadmap leads to successful implementation and scale-up of integrated care. Therefore, the resulting research question is: ‘How, why, and under which context conditions does a co-created scale-up roadmap lead to adoption, implementation, and scale-up of integrated care?’. Methods: A realist approach is used towards testing the initial programme theory (IPT) in the three countries. The IPT draws on political science theory of the multiple streams model (MSM) adapted by Howlett and includes five streams (problem, solution, politics, process and programme) that can emerge, converge and diverge across all policy stages. To test the IPT, information from different sources was collected. Firstly, qualitative interviews were conducted with the researchers in the SCUBY country teams as well as with key stakeholders (health facility managers, policy makers, civil servants, professional medical and patient associations, NGOs, and implementers). Secondly, a document review of grey literature, meeting reports, and official documents was performed. Finally, a workshop was organised with SCUBY researchers from all country teams to refine the IPT. We used the Intervention-Context-Actors-Mechanism-Outcome (ICAMO) configuration to synthesise information into a configurational map. Results: In each country case, the project partner’s mandate was key in the approach to scale-up, the design, and content, ...