Sustainability has been characterized and explored mostly from an environmental standpoint, with relatively less attention paid to social and economic dimensions. Because many sustainability organizations have grown out of the environmental movement, they tend to emphasize environmental priorities and retain many of the organizational strategies that were pioneered when the focus was on environmental conservation. However, to attain a more socially and economically informed environmental practice, broader procedural aspects, including recognition and participation, and substantive aspects, including issues of social need, distribution of wealth, and economic opportunity, need to be addressed as these matters are intimately linked to environmental concerns. In this thesis, I examined sustainability organizations against the concept of ‘just sustainability’, with specific consideration paid to uniting the substantive concerns of sustainability with the procedural concerns of environmental justice. I focused my examination on model forests and UNESCO biosphere reserves located in the Maritime Provinces of Canada, an area of high economic vulnerability and low political power. By looking to governance directives from environmental justice, entrepreneurship, and community development, I conducted a multi-case study analysis with organizations that have a mandate to address the environmental, social and economic imperatives of sustainability. Through engaging these organizations in a comparative learning situation, I was able to achieve the following objectives, to: i) assess the governance strategies used within these organizations against just sustainability theory; ii) understand the challenges faced by place-based organizations and examine strategies to better improve local understanding, community empowerment, as well as sustainability outcomes; and iii) assess the feasibility - conceptually and empirically – of incorporating social entrepreneurship into the governance practices of sustainability organizations to bring together the benefits of both approaches. The findings of this thesis make valuable contributions to the empirical evidence needed to advance our understanding of just sustainability, both conceptually and in practice. Overall, my findings point to the importance of understanding and improving our practice of sustainability governance through identifying and offering examples of innovative governance arrangements that are better able to address procedural and substantive concerns. Findings show that the stakeholder model typically used by biosphere reserves and model forests contributes to systemic challenges that limit procedural justice in these organizations. By looking to other literatures, including community development and social entrepreneurship, and to lessons learned from other place-based organizations, I propose ways to adapt governance strategies to improve community engagement and organizational outcomes, including a framework to inform place-based governance for just sustainability and a “hybrid model” that captures the benefits of stakeholder representation and social enterprise. This study speaks to the need for researchers and practitioners seeking to advance sustainability governance to extend their understanding beyond environmental sustainability to embrace more social dimensions. This thesis demonstrates the value of looking to broad literatures and new models to inform sustainability governance and encourage the adoption of new ways of thinking, new strategies, and new tools to help advance sustainability.