Thousands of ectomycorrhizal (ECM) fungal species exist, but estimates of global species richness of ECM fungi differ widely. Many genera have been proposed as being ECM, but ill a number of studies evidence for the hypothesized ECM habit is lacking. Progress in estimating ECM species richness is therefore slow. Ill this paper we have retrieved studies providing evidence for the ECM habit of fungal species and For the identification of the mycobiont(s) ill specific ECM associations, using published and web-based mycorrhiza literature. The identification methods considered are morpho-anatomical, characterization or naturally occurring ECMs, pure Culture synthesis, molecular identification, and isotopic evidence. In addition, phylogenetic information is also considered as a relevant criterion to assess ECM habit. OF 343 fungal genera for which all ECM status has been alleged, about two thirds have Supportive published evidence or ECM Status can be at least hypothesized. For the remaining taxa, Currently no indication exists as for their I-CM nutritional habit, besides field observations or associations with putative hosts. Our survey clearly indicates that current knowledge of ECM fungal diversity, as Supported by experimental evidence, is only partly complete, and that inclusion of many Funga genera in this trophic and ecological category is not verified at this stage. Care must thus be used when compiling lists of ECM and saprotrophic full studies oil the basis of published information only. On the basis of our literature search we conservatively estimate ECM species richness around 7750 species. However, oil the basis of estimates of knowns and unknowns in macromycete diversity, a final estimate or ECM species richness Would likely be between 20000 and 25000.