The primary intent of this thesis was to determine if and how the practice of Art of Hosting, a dialogue–based, participatory process architecture, could foster social capital in communities and other large, complex social systems working to address a variety of complex challenges, in order to draw conclusions that could contribute, in a meaningful way, to the advancement of strategic sustainable development (SSD). We hoped to gain useful insights by examining and interpreting the results from two case study systems existing within very different social contexts and with very different organizational structures: Columbus, Ohio and the European Commission. Based on the results of our research, strategic recommendations, guidelines and tools were developed for SSD practitioners wishing to assess the level of social capital in the systems in which they operate and take strategic steps to increase it. These same recommendations, guidelines and tools should also be helpful for Art of Hosting practitioners working to address complex societal challenges in general. Overall, the authors of this thesis believe that these results hold particular significance for any collaborative or multi-stakeholder effort to build support for adoption, and ensure the successful implementation, of sustainability goals and programs. This could include Eco-Municipalities, Transition Towns, Agenda 21 Communities, Smart Cities, and large complex organizations such as multi-national corporations or universities, to mention but a few.