Integrating governance analysis with behavioral economics suggests that the sustainable reduction of tax collection costs does not rely primarily on intensifying costly measures—such as traditional audits, inspections, and heavy coercive penalties—but rather on redefining the relationship between the state and taxpayers by aligning social norms with conventional behavior. Within this framework, if the state can enhance perceptions of "procedural justice" and public trust through procedural transparency, information symmetry, and institutional accountability, it can activate taxpayers' intrinsic motivation and internal ethics. Consequently, honest tax payment evolves into a "conventional and socially accepted behavior." Accordingly, this study aims to develop an integrated model of governance and conventional behavior for reducing tax collection costs, employing an approach that combines behavioral economics with governance analysis. A mixed-methods (qualitative-quantitative) research design was adopted. In the qualitative phase, a systematic literature review was conducted; out of 75 reviewed articles, 29 were selected as the basis for identifying indicators, resulting in the extraction of 17 distinct indicators. Subsequently, in the quantitative phase, Interpretive Structural Modeling (ISM) was utilized to construct the model. Data for this phase were gathered using self-interaction matrices, which were completed by 19 subject-matter experts. As a result of analyzing the collected data using the ISM software in MATLAB, a five-level model was derived, in which the most influential indicator is the clarity, symmetry, and overall transparency of information.