This paper presents initial results from field work on immunization coverage as part of improving health care policy implementation in Uganda. System Dynamics modeling and case study research methods have been used to capture the complex and dynamic nature of the immunization process, to enhance the understanding of the immunization health care problems and to generate insights that may increase the immunization coverage effectiveness. Field studies have been conducted to establish the operational immunization policy issues of concern to health care management which included capturing reference modes for the key variables and developing causal loop diagrams to illustrate the dynamics among key variables. The paper suggests an initial model that could be used for theory building in immunization policy evaluation.