It is the nature of powerful ideas that they can summarize a ground-breaking concept in a plain and simple message. In this sense, the concept of sustainability is a very powerful idea. However, although the sustainability debate has already brought about considerable conceptual progress, a pivotal dimension to sustainable development has so far been widely neglected. This article argues that in addition to the ecological, economic, and social dimension, sustainability critically depends on the moral dimension of institutional legitimacy. Against the backdrop of globalization, conventional models of creating and legitimizing institutions are increasingly challenged. Therefore, it is also business that is to play an ever more important role in contributing to fair and functioning institutions. The article discusses "corporate citizenship" as an economic concept as a useful starting point for this new understanding of the business of business. In effect, the underlying objective of this paper is to present a theoretical link between the concepts of sustainability and corporate citizenship. The central thesis is that private enterprises who cooperatively take responsibility for their institutional environment strengthen the moral dimension of institutional legitimacy: They actively contribute to empowering sustainability by corporate citizenship.