The database of chemical, mineralogical and physical characteristics of North American Fly ashes, assembled by the WFARDDC in North Dakota, was analyzed using multivariate statistics. Prior to the multivariate analysis, the data were rearranged in subgroups containing information on bulk-chemistry, glass chemistry, mineralogy and ASTM physical test results. These groups were analyzed individually. The multivariate technique used was Fuzzy C-Means Cluster Analysis, combined with Non-Linear Mapping. Analysis of the data-set indicates a relation between glass network former and network modifier content. The database shows that a subdivision on the basis of bulk CaO (< 11%; 11–20%; >20%) correlates well with the ASTM C618 Σ(SiO2 +Al2O3 +Fe2O3) and/or specific gravity. Mineralogical data indicate a subdivision into clusters containing varying amounts of mullite, quartz and/or ferrite spinel and a variety of Ca-containing minerals; high CaO ashes usually have high Ca-mineral contents. Of the CaO containing minerals, only portlandite contributed slightly to the compressive strength as defined by ASTM C618. Analysis of glass chemistry reveals smaller differences in absolute amounts of major oxides than would be expected on the basis of bulk chemistry alone. Surprisingly, the total glass content does not contribute significantly to 28 day compressive strength; multiple regression analysis only indicates a significant relation of particle size and specific gravity with the ASTM Pozzolanic Activity Index (portland cement). The Pozzolanic Activity Index with lime seems to be of limited importance in evaluating the performance of fly ashes as mineral admixtures in concrete. On the basis of the statistical analysis, suggestions for selection of important classifying variables are made.