The fair use defense in copyright law shields an intellectual commons of protected uses of copyrighted material from infringement actions. In determining whether a given use is fair, courts must assess the new use\u27s potential effect on the market for the copyrighted work. Fair use jurisprudence too often fails to address the complementary, network, and long-range effects of new technologies on the market for copyrighted works. These effects parallel the indirect, direct, and option values of biodiversity recently recognized by environmental economists. Their sophisticated methods for valuing natural resources in tangible commons can inform legal efforts to address the intellectual commons\u27 effect on the market for copyrighted works