Sustainability and economic growth—the integration and balance of social, environmental, and economic needs—is a salient concern for sustainable development and social well-being. By focusing on a sustainable innovation project, we explore how entrepreneurial ecosystems become sustainable entrepreneurial ecosystems and investigate the interactions of entrepreneurial actors. We conducted an inductive, single-case study of a specific collaborative innovation project in the denim industry specialized in a specific geographic location. From our data, we show that the presence of four conditional aspects foster sustainable entrepreneurial ecosystems. These include sustainability orientation of actors, recognition of sustainable opportunities and resource mobilization, collaborative innovation of sustainability opportunities, and markets for sustainable products. We make two observations that contribute to the literature. First, we see that in a sustainable entrepreneurial ecosystem, entrepreneurial experimentation is a highly interdependent and interactive process. Second, we see that recognition of sustainable opportunities is distributed among different actors in the ecosystem. Our findings also have implications for practitioners and policy-makers.