The lichen family Trichotheliaceae is a common component of the crustose lichen flora in tropical forests all over the world where they grow on tree trunks, leaves and rock outcrops. Until 1987, only 13 species of the family had been reported from the Guianas of which three are shown below to belong to other families. For this fascicle, about 300 collections, corticolous, foliicolous and some saxicolous lichens, from the Guianas were available for study, most of them recently collected in the framework of the Flora of the Guianas project. As presently understood, the family comprises three genera with ca. 200 species, most of which are poorly known. The neotropical representatives are estimated to number 100 species. All three genera have been found in the Guianas, where they are represented by 34 species, most of which have a pantropical distribution.