The anamorphic fungal genus Septoria is one of the largest of plant pathogens, causing a range of disease symptoms including leaf and fruit spots in agricultural crops, as well as horticultural and native plants. These fungi are known to infect hosts in 54 families of flowering plants in Australia, most notably the Asteraceae (daisies and their relatives) and the Poaceae (grasses). This authoritative account, the first overview of the Australian taxa, documents 132 species of Septoria, its telemorph Mycosphaerella and six related genera. Eleven species are described as new to science, and 64 names are regarded as doubtful or are excluded from the Australian mycota. A comprehensive introduction to Septoria and its allies is followed by detailed descriptions and illustrations of each taxon.