In recent years, the growing inequality of wealth has led to an increasing interest in taxes levied on it, both from the academic field and from fiscal policy. In this context, the Spanish case is particularly relevant due to the coexistence of several tax figures that tax wealth. Moreover, in Spain, the institutional context of fiscal decentralisation implies that taxes such as the Wealth Tax or the Inheritance and Gift Tax are devolved to the autonomous communities. The objective of this thesis is to analyse wealth taxation in Spain, considering three complementary dimensions: the taxation of large fortunes, the integration of the Wealth Tax into the Personal Income Tax, and the taxation of inheritances and gifts. In doing so, the functioning and effects of these taxes, as well as their possible reforms, are evaluated. Through the use of administrative microdata, both at the national and regional levels, microsimulation techniques are applied, combining ex ante evaluation with ex post analysis. Through these quantitative techniques, both the potential effects of reforms and the observed response of taxpayers are analysed. Specifically, the first chapter provides an analysis of the recent Temporary Solidarity Tax on Large Fortunes and its territorial revenue impact. The second chapter examines various reform proposals based on the integration of wealth taxation into the Personal Income Tax. Finally, the third chapter analyses how the regional reforms approved in the Valencian Community in the Inheritance and Gift Tax have affected taxpayer behaviour. Among the main results, it is observed that the effective taxation of wealth in Spain is largely conditioned by fiscal decentralisation. In particular, territorial differences in the regulation of certain tax benefits, such as reductions in the tax base and tax credits, give rise to marked differences in the taxation applicable to wealth and to gratuitous transfers. These differences focus the debate on fiscal competition to the bottom in Spain and on the need for harmonisation in wealth taxation to ensure a minimum and more homogeneous level of taxation across territories. With the aim of alleviating this issue, the central administration approved at the end of 2022 the Temporary Solidarity Tax on Large Fortunes. This state tax, initially temporary in nature, although subsequently extended, seeks to homogenise the taxation of large wealth holdings. However, the ex ante evaluation of this tax shows that its impact depends largely on the regional regulations of the Wealth Tax, since in its first year of application it presented a greater revenue effect in those autonomous communities that had established significant tax benefits in this tax. Regarding reform possibilities, the integration between wealth and income emerges as an alternative to the current system that improves both revenue and progressivity. This model of joint taxation has been applied in different countries under various forms and, at present, a system of this nature can be observed in the case of the Netherlands. Finally, it is found that gifts react strongly to fiscal changes, while inheritances show lower elasticity. In this regard, it is highlighted that taxpayers’ behavioural responses condition the real effectiveness of fiscal reforms in taxes levied on wealth. In summary, it is shown that the institutional design of these taxes is as important as their theoretical justification. Through an integrated evaluation of the current system of wealth taxation in Spain, this thesis provides relevant empirical evidence for improving the design of taxes levied on large wealth holdings and for the development of reforms aimed at improving the current tax system. The main implications derived from this thesis point to the need to review the overall taxation of wealth in Spain, improving coordination between tax figures and levels of government. Likewise, the reform proposals analysed show the usefulness of exploring alternative designs that integrate the taxation of income and wealth into a single tax figure. Finally, the importance of considering taxpayer behavioural responses in future fiscal reforms is emphasised, both in taxes levied on wealth and in those levied on gratuitous acquisitions.
