This chapter includes an experimental study elucidating the hypothesized that multivariate fuzzy-MCDM, but not classic MCDM, provides an intermediate assessment between strictly sustainable (membership 1) and purely unsustainable (membership 0) systems. The overall objective was to review the principles of Fuzzy sets and Fuzzy logic and then discuss the application of Fuzzy models in characterizing the social, environmental, and economic sustainability of natural and anthropic ecosystems. The analytical procedures to assess sustainability are described.