Sustainability problems are today becoming more prevalent, more systemic and more serious than ever before. And they are expanding, from operational inconveniences that could largely be addressed through line-level fixes, to boardroom enigmas and political groundswells that defy traditional boundaries. This paper argues that these shifts in the nature of sustainability problems are highly significant for researchers as well. They indicate that the ontology of sustainability issues is also shifting: it is growing increasingly complex. We can no longer speak meaningfully about social, environmental and economic sustainability issues as isolated, independent incidents. With growing acceptance that “everything is connected to everything else”,1 we recognize that we must progress beyond sole use of conventional reductionist epistemologies. Growing complexity is not a descriptive term, but rather an ontological watershed between classical Newtonian assumptions of linearity, stability, and reductionistic inquiry on the one hand, and nonlinear, self-organizing, and emergent complexity theory on the other. While readers of this journal are likely to be well aware of these changes, there is value in a careful examination of this apparent shift toward complexity-based inquiry in sustainability research. Indeed, there are dangers in not doing so: not only is conventional research growing more limited for revealing the nonlinear nuances that increasingly make up sustainability problems, but further, it may obscure the actual dynamics and dynamic elements in play in a given situation.2 Hence, there is a need to both distinguish the two approaches from each other, and to highlight how each may be better suited to address particular problemscapes, or econo-social-environmental systems situated in space and time.3 This paper attempts to address the above situation in three ways. First, in a brief review of current literature, it finds several types of confusion in conventional research and research calls. Second, it offers a distinguishing framework that clearly differentiates complexity-based sustainability from conventional views, and shows how both are valuable but each is incommensurable. Third, it presents an original, longitudinal and quantitative case study of a sustainability initiative in a UK organization, using competing hypotheses from each perspective. Results are unexpected and anomalous from a conventional perspective, but these “negative” findings may be interpreted as consistent with a complexity perspective on the organization and initiative. In sum, the neoclassical, positivist, and reductionist model of sustainability is certainly not the only, and may not be the best way to study internal organizational shifts towards sustainability. From literature to theory, and theory to practice, it appears that complexity perspectives are fast becoming the “there” needed in sustainability inquiry in order to get to the “here” of today’s sustainability issues and problems.