The first decade of the 21st century marked an important period in global demographics. For the first time in human history more people were living in urban than in rural areas. Rural and urban regions are closely intertwined and shaped by an ambiguous relationship. Rural regions are important deliverers of resources such as food, construction materials or energy and are thus enablers of these urban lifestyles. Rural regions are also places of aspiration and desire for a life closer to nature or in search for “wilderness” or “authenticity” of rural lifestyles, which people from cities would like to explore and experience during their visits. This ambiguous relationship is increasingly felt in rural regions in multiple ways e.g., through emigration of young people, the loss of jobs and economic possibilities, or the exploitation of land and infrastructure for businesses, enabling the flow of resources and capital into cities. Rural regions are therefore confronted with numerous challenges. For these regions it becomes important to continuously re-define or re-invent themselves in an increasingly urbanized and economized world, by at the same time protecting their natural assets and beauty and enabling both ecologically, socially and economically sustainable lifestyles. This publication aims to provide comprehensive information on the importance of social capital to achieve long lasting sustainable development that brings prosperity to rural areas. Sustainable development in this context is understood as positive development in all three dimensions of the sustainability triangle, namely economic, social and environmental. All of them equally important to create prosper rural areas with the ability to thrive. Social capital is the glue that helps people to organize themselves in groups in order to achieve socioeconomic benefits for the whole community. However, while the significance of social capital for economic and social development has been covered extensively in literature, the specific role it plays for sustainable development of rural areas at large could and should be further explored. For this, both theoretical and practical information is provided with eight illustrative case studies from Austria, Spain, Portugal and Türkiye that serve as best practice examples. These case studies show how communities achieve positive development in all three sustainability dimensions through the strengthening of social capital. At the end of the book, we discuss the significance of social capital for the success of these case studies and present a new definition of social capital that integrates the economic, social and environmental dimension.