Ecological economics, developed in the late 1980s, came to be known as the multi- and transdisciplinary science of sustainability. Since that time, it has blended basic and applied research with the intention of both informing and bringing change to environmental policy, governance, and society. However, many conventional economists have questioned its originality and contributions. This paper begins by clarifying the foundational perspectives of ecological economics that it engages an economy embedded in both real and limited ecosystems as well as socially constructed power relations. Herman Daly, a founder of the field, expanded on Nicholas Georgescu-Roegen’s entropy economics by focusing on a quantifiable sustainable scale of the economy and achieving justice in the control and distribution of economic benefits. He called for both quantitative analyses of economic scale and discursive approaches to a just distribution. The paper then discusses how the terms entropy, scale, and justice are used and interact in the literature, illustrated by some of the key debates in the field involving the Ecological Footprint, substitutability of natural and manufactured capital, and the growth—“agrowth”—degrowth debate. The debates also illustrate the potential for the field to influence policy. Ecological economics as the science of both sustainability and transformation can deploy numerous concepts and tools to provide insights on how to illuminate and solve some of the most pressing problems of the Anthropocene.