Recent results from large-scale DNA sequencing projects have shown that most biodiversity on earth is actually very small, represented in insects and microbes. The kingdom Fungi forms a highly diverse, relatively unexplored lineage of eukaryotes that shares a common ancestor with animals. Both comprise heterotrophic organisms, but Fungi form (chitinous) cell walls and are exclusively osmotrophic; that is, nutrient uptake is extracellular. Although nearly 150,000 species of Fungi have been described, between 2.2 and 3.8 million are estimated to exist. Many habitats, ecosystems and host plants have, however, never been investigated, and thus their microbial inhabitants remain unexplored, unknown, and underutilised. Over the past 10 years, mycologists have on average described 2000 species per year, meaning that it will take more than 1000 years to simply describe the number of fungal taxa we estimate to occur on earth. Phytopathogenic fungi are important agents of plant disease, resulting in major annual losses to agricultural and forestry industries. The Dothideomycetes and Sordariomycetes are two of the largest and most diverse classes of ascomycete fungi, with thousands of phytopathogenic species comprising an incredible diversity of lifestyles, many of which have evolved multiple times. Studying their evolution has significant implications for our fundamental understanding of fungal evolution, and practical implications regarding the effects of climate change on these pathogens in agriculture. The availability of whole-genome data produced a high-confidence overall phylogeny of these classes, providing a clearer picture of the relationships among the various families, indicating that pathogenicity evolved multiple times within this class. Within Dothideomycetes, ancestral character state analyses support a terrestrial saprobic lifestyle as being ancestral within the class, also at ordinal and family levels, and that several transitions have occurred to evolve lichenised, plant and human parasitic, ectophytic (sooty blotch and flyspeck) and more recently epiphytic (sooty mould) lifestyles.