Support for land preservation is in large part rooted in the conviction that present generations have an obligation to benefit future generations by affording them the opportunity to enjoy and appreciate environmentally sensitive lands. The recent emergence of perpetual restrictions on land use as a popular conservation strategy, however, means that land preservation often involves the deliberate attempt to restrict the options available to future generations. Commonly known as conservation easements, these perpetual restrictions are designed to limit or prohibit the development of land, thereby preventing those who come after us from making their own decisions regarding both land preservation in general and the value of particular parcels. This paper explores the tension between preserving nature and ensuring that future generations have sufficient flexibility to respond to advances in scientific knowledge and changes in cultural values.