Healthcare budgets are limited, and decisions must be made about which healthcare technologies should be funded from these limited budgets. Decision makers rely on clinical and cost-effectiveness evidence on which to base their decisions, the gold standard vehicle for this evidence is a clinical trial. Guidance exists for conducting economic evaluations alongside clinical trials using standard treatment arm-based comparisons to assess cost-effectiveness, however because of differences in the purposes of the clinical effectiveness and cost-effectiveness analyses this conventional treatment arm-based economic evaluation is often uncertain. Furthermore, economic evaluations focus on the final cost-effectiveness summary measure without consideration of what is driving this measure. There is scope for providing a more detailed understanding of the conventional cost-effectiveness results. Conceptual models are simplified versions of real-life systems in a visual format, illustrating how key components of the system are linked and interact within it. In the field of economic evaluation conceptual models are recommended for and used as a guide to establish the structure of decision analytic models, in other fields they are also used as a communication tool, to aid understanding of the system and to give direction to research. The aim of this thesis was to expand the role of conceptual models in economic evaluation. This thesis proposed a new role for conceptual models to provide additional understanding to decision makers, extending the conventional economic evaluation analysis beyond a treatment arm-based analysis. This role was demonstrated using two case studies as illustrative examples, aiming to show how the role could be applied. This thesis demonstrates the value of an additional conceptual model driven analysis to supplement the conventional treatment arm-based analysis, adding further insight into the trial mechanism and what is driving the economic evaluation results. The contribution of this thesis to the field of economic evaluation is twofold; a new role for conceptual models in economic evaluation and a methodological framework for developing conceptual models in this new role