Sustainability issues are typically characterized by high complexity and uncertainty. In light of this, communication plays a crucial role in coping with these challenges. The previous debate on sustainability communication has largely focused on how to communicate sustainability issues to others. Sustainability communication, however, involves more than sender oriented communication to persuade others (“communication of sustainability”); it also embraces processes of dialogue and discourse (“communication about sustainability”). Based on this distinction, we develop a typology of communication modes, including communication for sustainability. Inspired by the notion of functional communication systems, we explore sustainability communication in six societal subsystems, applying the typology of communication modes. Drawing mostly on examples from Germany, we find a shift from “communication of” towards “communication about” sustainability in most subsystems. While communication subsystems have a tendency towards operational closure, a variety of interlinkages exist. We discuss three key areas of “opening up” communication subsystems, leading to transdisciplinarity, societal deliberation and governance, each meeting one of sustainability’s core challenges.