A brownfield is developed land (such as a factory site, railroad siding, or former military base) that is now underused – often vacant or derelict, and sometimes contaminated or feared contaminated. While the market will usually ‘recycle’ land whose former use has become obsolete in some way, brownfield properties are ‘stuck’ in an underused state. The market, left to itself, will not recycle them into more active use, often because the perceived cost and risk of bringing them back into use exceeds the benefits to owners. The broader urban and social costs of these underused ‘holes’ in the urban fabric are great, and would often justify the necessary expenditures. Land in central and accessible locations lies non-productive, in terms of the urban fabric and municipal revenues, while marring the contiguity and desirability of adjacent properties. To eliminate the barriers and market failures that prevents such land from reentering into productive use, some kind of public sector intervention (finance, coordination, regulatory change) is often necessary.