The dissertation is devoted to solving the current scientific problem of improving the theoretical and methodological foundations of the formation of the country's tax competitiveness in the conditions of shadow economy. A retrospective analysis of the development trends of the components of the tax competitiveness of the country was conducted, which allowed to generalize the peculiarities of the functioning of the tax system of Ukraine and certain countries of the world. The results of the analysis of the drivers of the formation of tax competitiveness of Ukraine proved that for a sufficiently small number of tax payments, the duration of tax reporting and tax payment is one of the highest in the world; the implementation of export and import operations is time-consuming and expensive; the general level of the tax burden is one of the highest in the world, and the changes made to regulatory acts on taxation are inconsistent and non-systematic in nature, deepen the inconsistency of the norms of individual regulatory acts and generally do not meet the principles of sustainability and coherence. A scientific-methodical approach based on a combination of tools of correlation-regression analysis, the Fisher method, and the multiplicative convolution method, which made it possible to assess the level of the country's tax competitiveness as a comprehensive indicator that takes into account process, institutional, moral-ethical and economic components was developed. Considering the calculated values of the country's level of tax competitiveness, 3 clusters of countries were selected using hierarchical and non-hierarchical (k-means methods) clustering. Within them, based on the analysis of the features of the construction of the tax system, the comparison of marginal and average values, criteria for the identification of competing countries and those with common trends in the development of the tax system were formed. The paper analyzes the main trends in the functioning of the shadow sector of the economy, which made it possible to deepen the theoretical foundations of the study of the impact of the shadow economy on the country's tax competitiveness. Based on the selection of the main forms and the consequences of the manifestation, the most important income shadowing operations from the point of view of impact on the level of tax competitiveness of the country - informal production, informal employment, activities carried out by firms without registration were selected. This formed the basis for the development of a theoretical and methodological approach to modeling the influence of the shadow economy on the integral level of the country's tax competitiveness, which comprehensively combines the application of regression analysis methods, Shapiro-Wilk tests, and Spearman's rank correlation. As a result, eleven econometric models of the formalization of the influence of indicators of the functioning of the shadow sector of the economy on the level of tax competitiveness of the country were built. It has been proven that informal employment of the population exerts the greatest influence on the level of tax competitiveness of the analyzed countries of the world. A methodological approach to the formalization of functional dependencies between the levels of tax morality and tax competitiveness of the country, which is based on a combination of tools for descriptive analysis of data series, analytical methods, and econometric analysis has been developed. It has been proved that there is a long-term unilateral influence of tax morality on the level of tax competitiveness and shadowing of the economy. Through the construction of a system of structural equations, an analysis of the coherence of the growth of the country's tax competitiveness and the detinization of the economy under the influence of the institutional environment was carried out, the influence of indicators of the quality of the institutional environment on the level of the country's tax competitiveness and simultaneously on other components of the Index of the quality of the institutional environment was modeled. According to the simulation results, it was established that the Government Efficiency Index and the Corruption Control Index exert the greatest influence on the quality of the institutional environment in Ukraine. Based on the construction of models with fixed or random effects, a scientific and methodical approach to the formalization of the dependence of the level of tax competitiveness on the level of introduction of digital technologies has been developed. It has been established that the Digital Economy and Society Index, Digital Evolution Index, Global Innovation Index, and Economy Digitalization Index exert the greatest influence on the level of tax competitiveness.
