The question of the relation between the aims of current federalism and welfare states has often been portrayed as the idea of two dynamics addressing divergent senses: while federalism would essentially imply centrifugal tendencies, the fulfilment of welfare state postulates would require certain social standardization processes. However, the viewpoint from which this work departs is the constitutional intertwining of both concepts: it sets out to analyze how the welfare state principle and the federal territorial structure are constitutionally interrelated. In particular, the aspect of welfare state that is tackled refers to its fulfilment on a nation-wide basis, which requires focusing on the mechanisms needed to generate certain levels of socio-economic standardization. The main theme of the dissertation is therefore the analysis of the structural elements that embody the territorial scope of solidarity within the context of two politically decentralized countries, Germany and Spain. The dissertation is structured into five chapters. Chapter One, after analysing how the concepts of “welfare state”, “federalism” and their “interrelations” are tackled and explained by the existing literature, outlines an analytical framework for the examination of the territorial translation of welfare state. Chapter Two addresses the constitutional articulation of the search of a basic equality on the whole territory from the perspective of the allocation of social competences – i.e. health care, social assistance and social security and education - both in Germany and in Spain. Chapter Three focuses on some of the “constitutional structures” that are in charge of guaranteeing the basic uniformity of living conditions throughout the territory of each country (e.g. Art. 72 of the German Basic Law and 149.1.1 of the Spanish Constitution). Chapter Four analyses certain mechanisms that articulate the financial territorial redistribution in each system. Chapter Five is devoted to analysing the EU as a new territorial stratum involved in the social sphere regulation interacting with the nationally based welfare state.