Introduction: HIV/AIDS and Noncommunicable diseases (NCDs) are major diseases of publichealth significance worldwide, especially in developing countries, and increasing research has reported important relationships between them. Recently, there is emerging evidence suggesting strategically important similarities between health system responses to these conditions and thus the need to consider more integrated approaches in the future. Such integrated approaches can maximize synergy and improve efficiency of response. However, the evidence base to inform this approach is limited. Therefore, there is an urgent need to conduct more research in relation to such an integrated approach in the context of health systems of low and middle income countries.Aims and objectives: The aims of this PhD research were to analyse the interrelationships(Convergence, Linkage, Co-occurrence and Parallels) between HIV/AIDS and NCDs; and to develop a model and a guiding tool to inform implementation of a more appropriate responses by health systems to HIV/AIDS and NCDs in the context of developing countries.Methods: The overall PhD research was a - Health policy and system research that employed apragmatic mixed method and modelling techniques based on the constructivist approach. In thisresearch, different methods were applied at different stages. To analyse connections betweenHIV/AIDS and NCDs, four methods were used: Correlational and cluster analysis (for convergence), framework development using thematic research synthesis (for linkage),systematic and critical reviews (for co-occurrence), and qualitative content analyses (forparallels). For the development of action model, multi-level (integrative, configurative andinterpretive) evidence syntheses methods were applied. The integration tool was formulatedbased on the action model from best available evidence and was conceptually validated throughfurther literature review and expert consultations.Results: With rapidly increasing NCD magnitude and stabilizing HIV epidemic, many low-andmiddle income countries are facing an overlapping double burden of HIV/AIDS and NCDs. Theoverlap, however, is different in the Sub-Saharan African and Asian Context. After identifying two forms, two types and six pathways of epidemiological linkages between HIV/AIDS and NCDs, a Public Health framework illustrating these linkages was developed. The magnitude of NCD comorbidities in HIV infection was high for cardiovascular abnormalities and precancerous lesions with the dynamics being highly reverted by the scale-up of anti-retroviral treatment coverage. The responses to HIV/AIDS and NCDs, both at Global and National levels, are similar in models and approaches. However, they are different in content. In this PhD research, an action model and a guiding tool for integration are also developed. Finally, evidence about the rationale, policies and models relevant to HIV-NCD integration is consolidated systematically.Conclusions: The strength of inter-relationships between HIV/AIDS and NCDs and the similarities between the responses to these conditions require improved and integratedresponses as appropriate to specific local contexts. In addition to generating evidence relevant to HIV-NCD integration, this PhD research has yielded three important research outputs - a public Health Framework for linkage, a model of integration, and a guiding tool for integration. Further research is needed to refine these outputs and to test their applicability in specific contexts.