Although 'environmental justice' is an increasingly important issue for policy makers and researchers, it remains for many a vague and abstract notion that is hard to define in practical, real-world terms. Part of the problem is that environmental justice is a complex, multidimensional construct that cannot easily be defined. Our aim in this article is to identify fundamental dimensions of environmental justice and highlight the resulting questions that are an inherent part of putting principles into practice. We argue that to have a constructive and informed debate about this emotionally charged topic, it is necessary to have a clear and workable definition of environmental justice. We do not propose our own definition, but instead point out that there are many possible legitimate definitions depending on one's beliefs, opinions, and values. The central point is not that a particular definition is right or wrong, but rather than choosing a definition has distinct implications for the formulation, implementation, and evaluation of both policy and science. These critical choices should be made explicit so that public dialogue can focus on the substance of this important policy issue.