Purpose: This paper makes an early attempt to extend the capability perspective to the area of sustainability innovation (SI) development by conceptualizing SI capabilities developed by best practice companies. Methodology: A qualitative in-depth multiple case study methodology has been used. SI approaches of five leading companies in developing sustainable innovation projects has been identified and correspondingly, how different approaches develop different capabilities (namely; networking capability, learning capability, innovative capability) are analyzed by detailed case and cross-case analysis. Findings: The results show that although all SI firms develop basic mechanisms for developing each capability, “sustainability-rooted” firms, who embed sustainability in their core strategy, even go beyond traditional “innovation-based” firms by establishing further mechanisms. This leads sustainability-rooted firms to possess higher level of all three capabilities even innovative capability. More specifically, the mechanisms which different approaches use for developing each capability are identified. Relevance: The paper is theoretically relevant by integrating the existing literature to develop a testable framework. From a managerial perspective, a key question that firms, engaging in sustainability, face is how to build and leverage firm's capabilities to enhance sustainability. Our results will help managers to deal with the challenges they face in carrying out this path.