The present thesis aims to explore the role and the evolution of tax and fiscal integration (and by implication, a central component of economic integration) from a legal perspective. "Integration through fiscality", as perceived in this dissertation, comprises two components: direct taxation and fiscal policies (the public finance management of the Member States). The present thesis sets out by pointing to the paradox that, despite their central role in the attainment of an 'economic union without frontiers', 'fiscal matters' remain without any solid constitutional framework. After demonstrating the lack of a "constitutional fiscal framework", the thesis proceeds with an 'actors' based' historical account, through the turning points of European Economic integration (Pre- Maastricht, Post-Maastricht and financial crisis). This narrative aims to show the inter institutional struggles among the different actors (the legislator, the Member States, the executive and the judiciary) in their bid to fill this lacuna in the European (Economic) Constitution, through distinct or sometimes parallel ways. To this end, the thesis primarily gives the institutional and constitutional background of 'fiscality', while it continues by analysing the different possibilities of integration through 'fiscality': a) positive integration through the legislator via hard or soft law means, b) spontaneous integration triggered by regulatory competition and the Member States, c) 'coordinated' integration prompted by the Member States, d) negative integration prompted by the CJEU, e) crisis-induced integration outside or within the EU law framework, f) integration by 'force', g) integration by exception. The thesis maintains that, notwithstanding the efforts of the CJEU that has risen as the key player pushing for integration in the area of the tax policy, it has been the recent financial crisis which has spurred the other actors towards more integration in the area of fiscal policies with the anticipated domino effects in the direct taxation field. The final part of the thesis attempts, by means of a normative claim, to sketch the salient features of a 'fiscal Constitution' for the EU, as part of the 'new economic governance construction', that will be both (politically) feasible and compliant with certain standards of legitimacy and the rule of law desiderata.