Introduction:The present study aims to design a good governance model with an emphasis on social capital in Iran's tax system. Given the structural and behavioral challenges of the country's tax system, on the one hand, weaknesses in governance mechanisms (transparency, accountability, and efficiency), and on the other hand, deficiencies in social capital (public trust and civic participation) have led to reduced tax compliance and erosion of institutional legitimacy. This research seeks a coherent response to the fundamental question of how an integrated model of good governance and social capital can be designed to enhance the acceptability and efficiency of Iran's tax system.

Methodology: This research is applied in terms of purpose and qualitative in terms of data collection method, utilizing a thematic analysis approach. The statistical population consisted of experts and specialists in the fields of taxation, public governance, and social capital. Purposeful (judgmental) sampling was employed, and data were collected through semi-structured interviews with 13 senior managers of the Tax Affairs Organization, university faculty members, experts from the Parliamentary Research Center, and independent researchers until theoretical saturation was achieved. Data analysis was conducted using the Braun and Clarke (2006) method at three levels: basic themes, organizing themes, and global themes. To ensure validity, strategies including participatory research, member checking, and peer review were utilized.

Findings: Analysis of qualitative data led to the extraction of 63 basic themes, 11 organizing themes, and ultimately 5 global themes. These five global themes are: (1) Participatory, Transparent, and Accountable Governance (comprising 14 basic themes and 2 organizing themes), (2) Efficiency, Adaptability, and Updating of Tax Processes (comprising 15 basic themes and 2 organizing themes), (3) Education, Awareness, and Human Empowerment (comprising 7 basic themes and 2 organizing themes), (4) Justice, Social Support, and Sustainability in the Tax System (comprising 11 basic themes and 3 organizing themes), and (5) Ease, Business Support, and Taxpayer Rights (comprising 16 basic themes and 2 organizing themes). The findings revealed that the realization of good governance in the tax system results from a balanced interaction among transparency, participation, accountability, justice, human resource empowerment, process improvement, and protection of taxpayer rights. Experts emphasized the pivotal role of transparency and trust-building as the foundation of institutional social capital and believed that these themes form an interconnected causal chain, beginning with legitimacy and acceptability, advancing to operational efficiency and agility, passing through the context of empowerment and awareness, taking root in justice and sustainability, and ultimately reaching the final point of contact with citizens' lives through dignity, support, and ease.

Conclusion: The present research has reached the fundamental conclusion that social capital in the tax organization emerges from good governance, and good tax governance depends on transparency, trust, participation, justice, and human dignity. The five-theme model presented provides a comprehensive and operational framework for redesigning the relationship between the Tax Affairs Organization and taxpayers and society, reminding organizational managers that good governance depends on shifting the perspective from a mere tax collector to a social, accountable, and empathetic institution. This shift in perspective becomes possible when the organization, beyond focusing solely on revenue, also considers shared values and the quality of relationships with taxpayers. In this horizon, tax transforms from an imposed burden into a social contract; a contract in which the organization and taxpayers, shoulder to shoulder and with mutual trust, step forward on the path of national development and progress. The proposed model can serve as a conceptual framework for planning, policy-making, and reforming the managerial structures of the Tax Affairs Organization, paving the way for the realization of good governance.