We model public relations as a specific form of strategic communication that plays a crucial role in the transformation toward sustainability that encompasses social, ecological, and economic aspects in equal measure. Such transformation is urgently needed because of the multiple crises that societies are facing worldwide. Drawing on existing literature, we discuss three different modes of the relationship between sustainability and public relations, namely (1) public relations about sustainability, (2) public relations for sustainability, and (3) the sustainability of public relations. Analyzing the interrelationship of these different modes, we reveal points of friction between them that must be acknowledged if the crucial role and responsibility of public relations in the transformation are to be impactful.