When one size doesn’t fit all: how national standards and scope choices fragment CSRD assurance

Purpose This study aims to examine Corporate Sustainability Reporting Directive (CSRD) assurance practices in the first year of implementation, analyzing how “structured fragmentation” and market innovation emerge within formally harmonized regulatory frameworks. Design/methodology/approach This study uses purposive content analysis of 100 sustainability assurance reports across 29 European countries for the 2024 financial year, using detailed manual coding to reveal patterns beneath surface-level compliance. Findings The analysis reveals two distinct phenomena. First, structured fragmentation: 87% of companies obtain only limited assurance using globally standardized language, yet these opinions rest on fundamentally different national legal frameworks, demonstrating legitimate decoupling through sanctioned national pathways. Second, market-driven quality differentiation: 11% of firms voluntarily obtain reasonable assurance on selected high-materiality metrics (greenhouse gas emissions, EU Taxonomy), creating strategic differentiation within regulatory uniformity. Research limitations/implications Analysis captures the inaugural CSRD year during the transitional period. Longitudinal research will assess whether practices converge following EU assurance standard adoption by October 2026. Practical implications Identical clean opinions may reflect different assurance approaches across jurisdictions. Mixed assurance demonstrates market opportunities for competitive differentiation within uniform mandates. Originality/value This study makes two theoretical contributions: introduces the structured fragmentation concept, showing how hybrid regulatory designs create legitimate decoupling during institutional transitions, and documents market innovation within mandatory regimes through voluntary assurance enhancement.