Informed by the neo-institutional perspective, this study seeks for the first time to investigate empirically the determinants of ISA adoption and commitment to harmonisation on a cross-national basis (89 countries). The findings show that the protection of minority interests, regulatory enforcement, lenders/borrowers rights, foreign aid, prevalence of foreign ownership, educational attainment and particular forms of political system (level of democracy) prevailing in a country, are observed to be significant predictors of the extent of commitment to the adoption and harmonisation of ISAs. Our statistical analysis therefore suggests that coercive, mimetic and normative pressure have a significant impact on ISA adoption relative to economic (efficiency-led) factors. Our findings imply that current efforts by the International Federation of Accountants (IFAC) and other international agencies to implement ISAs need to recognise that a broad set of institutional factors, rather than narrow economic ones, are of relevance in the development of audit policymaking, practice and regulation worldwide.