This study examines the continuities that can be found within the Spanish taxation system during the eighteenth century. Despite the War of the Spanish Succession and the Nueva Planta, the Bourbons did not abolish the taxation system inherited from the Habsburgs, but tried as far as possible to improve it. On the other hand, an examination of the eighteenth century reforms applied to economy and taxation allows the wider question of the roots of the Iberian Ilustración to be tackled from an original perspective. It stands to reason that the Ilustración was the result of the confluence of a plurality of traditions, currents of thought and branches of knowledge, old and new. Prominent among these were the proyectismo heir to the seventeenth-century arbitrismo; the persistent regalist tradition revitalized by the reforming trends within Catholicism ; natural law; and, lastly, political (or “civil”) economy, the scientific and academic status of which was defined precisely during the reign of Charles III thanks to the Sociedades Económicas de Amigos del País and the creation of the first university chairs in Saragossa. This (and other) theoretical systems were combined and hybridized by the ilustrados according to their political struggle and related reformatory planning – which was sometimes confused, but at other times was more coherent and effective: the aim was to correct some of the most evident injustices in the coeval class-based society. The vitality of the debates on the fiscal reform shows that a sector of the Spanish ruling classes tried to change the Old Regime society from the top, keenly aware of the link between the reform of the agrarian world and the shift of the levy from indirect taxes (excise taxes and customs duties) to direct ones weighing on real estate and incomes in general. If eventually the last generation of ilustrados (including the pro-Bonapartist afrancesados) and the first generation of Spanish liberals failed in the objective of strengthening the class of small landowners and tenants to whom they wanted to entrust the re-launch of the Iberian economy, this was the result of the capacity for resistance of the privileged classes, who proved to be refractory to change.