Ecological Economics inherently faces a challenge akin to sailing between Scylla and Charybdis. In Greek mythology these are two monsters located on opposite sides of a narrow strait, and falling victim to one or other of them is unavoidable. In the recurring process of establishing and refining its conceptual foundations, Ecological Economics runs the risk of, on the one hand, losing important insights by trying to be radically different from mainstream economics and, on the other hand, becoming a redundant appendix to mainstream environmental economics by routinely applying its concepts and methods. We argue that avoiding both fallacies is possible by using Ecological Economics' orientation towards sustainability as a guiding principle. The scientist's power of judgment supports her decision concerning which methods are suitable for tackling a given sustainability problem. The intersubjective quality of judgment prevents the resulting methodological pluralism from drifting toward arbitrariness.