Evaluating sustainability in forest management requires decision makers to consider multiple, conflicting definitions in an environment of risk, uncertainty, and incomplete or non-quantitative information. Zadeh's fuzzy set theory provides a rigorous, flexible approach to the problem of defining and evaluating sustainability and comparing alternative scenarios. We discuss how fuzzy set concepts can be used to better manage for goals such as sustainability, equity, and ecosystem health. We then show how a simple tabular technique using fuzzy sets can be used to compare management alternatives, incorporate multiple objectives, and identify knowledge gaps and areas of disagreement. The simplicity and flexibility of this technique provides needed support for more explicit, objective decisions.