In this paper we address two related conceptual and practical challenges in assessing "sustainability." The first is the criteria to be used, in particular the relationship between sustainability and measures of economic well-being and the use of monetary versus nonmonetary indicators. The second is the problem of determining which physical scales to use for sustainability assessments when there are multiple and overlapping "communities" or stakeholder groups. While neither set of challenges admits a definitive solution, there has been progress on the first set of issues - in particular, through the development of multicriteria assessment strategies and stakeholder involvement processes. In contrast, the problem of how to assess sustainability in practice at multiple scales remains less well understood.