Business incubators can be catalysts for sustainable development if they integrate sustainability into their mission of entrepreneurial support to start-ups, from selection to the end of the program. The focus on supporting sustainable entrepreneurship is a new phenomenon in business incubators. Unfortunately, the risk is that the integration of sustainability goals is merely a legitimization strategy rather than an established element of the incubator's activities. Hence, this study proposes a comparative case study of three business incubators who showed interest in sustainability to see to what extent this focus is integrated into their entrepreneurial support system.