Overconsumption remains a controversial topic in much discourse, and its definition remains hazy. Here we thus develop three definitions relevant to different scales—individual, social,
and planetary. These can be used to form overlapping corridors beyond which consumption can be defined as useless, unfair, and/or unsustainable, each of which justifies different political responses. While these definitions emerge from different literatures—not all of which are concerned with environmental sustainability—we describe how all can (and should) be integrated and related to environmental limits. We then discuss the implications for understanding and modelling sustainability transitions.