The consumption of natural resources by modern societies, the environmental and social impacts that are associated with it, and the possible pathways to reach more sustainable patterns of consumption, constitute a significant field of study in environmental, economic, and social sciences. With the majority of scientific researches approaching sustainability while keeping economic growth as a central prerequisite, the following research adopts an alternative pathway, connected to the concept of strong Sustainable Consumption. The research project aims to investigate how Greek society can be transformed towards strong Sustainable Consumption by the agency of the alternative economic model of Social and Solidarity Economy. The emergence of Social and Solidarity Economy in Greece, during the economic and social crisis that the country faced from 2008 onwards, presents itself as an opportunity to investigate how such an alternative economic system may contribute to the expansion of strong Sustainable Consumption. As there is a lack of scientific studies addressing the transition towards Sustainable Consumption under Social and Solidarity Economy, the present thesis provides innovative results that could lead to further research on the subject. For this purpose, the following research question was formulated: How do Social and Solidarity Economy initiatives in modern Greece contribute to the transformation of Greek society towards ‘strong’ Sustainable Consumption? An extensive literature review on the concepts of strong Sustainable Consumption and Social and Solidarity Economy, alongside an examination of the current practices of the latter in the country of Greece, are presented. The individual initiatives are chosen as the unit of analysis of the research design to study the social transition. The development of an analytical framework, based on the theoretical framework of Transformative Social Innovation, attempts to answer the formulated research question. Under this framework Social and Solidarity Economy is defined as a Social Innovation that is described as a change in social relations, involving new ways of doing, organising, framing and/or knowing. The framework investigates the levels of transformative change that such innovations can achieve, mainly their transformative ambition, potential and impact. The methodology proposed to implement the framework follows the multiple case study approach followed by a cross-case comparison. Based on the literature review on the state of Social and Solidarity Economy in Greece, it was revealed that cooperatives comprise the most active and legally contextualised form of Social and Solidarity Economy in the country. Consequently, the selected cases were cooperative ventures operating in different areas of Greece. The research results enrich the knowledge on the different ways that cooperatives develop new social relations and new ways to frame, organise, do and know Social and Solidarity Economy. The analysis revealed that all cases relate to strong Sustainable Consumption concepts or practices and they have accomplished some level of transformative change, while all cases exhibit traits that can be described as innovative and that challenge the dominant institutions of production and consumption that exist under the neoliberal context. Concerning the current contribution of Social and Solidarity Economy initiatives in the transformation of Greek society towards strong Sustainable Consumption, it can be concluded that is limited. While the ventures demonstrate attributes that can put forward the concept of strong Sustainable Consumption in the country, and indicate that they have transformative capacity, a broader transformation has not been identified yet.