Government, corporate and other decision makers are more and more often being urged to 'act sustainably' and to pursue policy paths toward 'sustainable development.' However, application of these concepts is hampered by serious interdisciplinary disagreements about the interactions of humans with their environment. Moreover, reducing disagreements about sustainability cannot be achieved solely through an improvement in scientific knowledge. These observations lead me to express skepticism about the capacity of any more or less mechanistic rule, economic, scientific or otherwise, to provide definitive and reliable answers about sustainable policies or conduct. However, there are processes and procedures that can help guide decision-making. I underscore the need for a methodologically pluralistic approach to addressing sustainability issues, while also underscoring the importance of addressing economic costs and benefits as one critical element of sustainability assessment. Practitioners of cost-benefit analysis are increasingly recognizing the need for embedding their findings in a broader set of information. A pluralistic approach, without mechanistic decision rules, only increases the need to have greater quantity and maturity of political discussion and education about sustainability than seems often to prevail.