Ecological economics is a relatively new interdisciplinary field concerned with the relationship between economic systems and the biological and physical world. This article covers the following topics: A discussion of views on whether ecological economics is just a field or approach within economics or a new ÒtransdisciplinaryÓ field in its own right; Origin of the name of the field; Core common principles of ecological economics; Comparison with environmental economics; Applications; History and institutions of ecological economics. The core principles are that the economy is embedded and dependent upon the ecosphere and that, therefore, models of the economy have to comply with biophysical principles. Ecological economists believe that there are limits to our ability to substitute human-made inputs and knowledge for natural resources and the environment in both production and consumption. They also argue that economic policy must consider jointly the objectives of economic efficiency, equity, and sustainability.