Corporate Sustainability (CS) links environmental and social issues to the corporate level by integration into conventional management. Thereby, companies can achieve sustainable organizational development and contribute to the sustainable development of society. One criterion of CS, among others, is eco-efficiency which aims to achieve environmental and economic excellence. By combining environmental issues with economic performance, aiming for eco-efficiency can be a practical starting point for small and medium sized enterprises (SMEs) reorienting their conventional management with small, not too radical steps. Considering the peculiarities of SMEs and inherent resource constraints, collaboration with intermediary organizations can promote this process. Through such collaboration SMEs have access to comprehensive and external expertise, can solve problems at the business level, establish new forms of partnerships and engage in learning networks. To identify the role of intermediary organizations in the process of aiming for eco-efficiency, this study chose a qualitative exploratory research using the multi-case study approach. Thereby drivers, barriers and matters related to adopting eco-efficiency through collaboration were identifiable. Owners and managers of SMEs operating in the metal- and mechanical engineering industries in Germany were interviewed. These companies took part in the ECOPROFIT®-scheme Germany, a partnership model between public and private organizations aiming to improve eco-efficiency. In this model local authorities act as intermediary organizations in terms of facilitating change and mediating between partners. The findings of this study suggest that eco-efficiency may be a suitable first step for SMEs to move towards CS as it presents a win-win situation. The role of intermediary organizations as initiators and facilitators to overcome challenges and barriers specific to SMEs is also indicated by the presented study.