The usual technical land evaluation procedures use Boolean logic based on crisp sets (yes/no) and sharply defined suitability classes. They ignore important aspects of reality caused by internal inhomogeneity and short range spatial variation, which can result in a considerable loss of information. Fuzzy set theory, which is a generalization of the classical set theory to situations were data are modelled by entities whose attributes have zones of gradual transitions, rather than sharp boundaries, offers a useful alternative to the conventional land evaluation methodology. Some basic principles of fuzzy set theory, and the choice of membership functions, weight values and fuzzy operators are explained. A comparison of results from using Boolean and fuzzy set methodologies for some case studies in China and Thailand highlights the advantages of the fuzzy set approach, although critical decisions are required on choice of membership functions and weights which have a major effect on the results. The weaknesses in the fuzzy set methodology and future research needs for its application in land evaluation are also discussed.