This paper proposes a platform for evaluating the relevance of IFRS in a prior-implementation context that may be of interest to any country concerned by the international accounting harmonization. Thus, in one hand, a tool is provided to measure the level of voluntary harmonization of local accounting practices with IFRS (voluntary de facto harmonization). In the other hand, the theoretical foundations that might explain such a measure are presented. In fact, the contingency theory and the neo-institutional approach helped us establish the explanatory variables, hypothesis and research models, related to two distinct local populations, involving the commercial firms and the accounting firms. Finally, we test the proposed platform for evaluating the relevance of IFRS in a prior-implementation context on the Tunisian case. We found that this emergent country is not yet prepared for an immediate transition to IFRS. Overall, the potential level of de facto voluntary harmonization is rather due to foreign institutional pressures that require IFRS as a reassuring and seducing label, than to a real local need.