The class Dothideomycetes is the largest and most ecologically diverse class of fungi, comprising endophytes, epiphytes, saprobes, human and plant pathogens, lichens, and lichenicolous, nematode trapping and rock-inhabiting taxa. Members of this class are mainly characterized by bitunicate asci with fissitunicate dehiscence, and occur on broad range of hosts in aquatic and terrestrial habitats. Since the last monograph of families of Dothideomycetes in 2013, numerous novel species, genera, families and orders have been discovered. This has expanded information which has led to the modern classification in Dothideomycetes. In this paper, we provide a refined updated document on families of Dothideomycetes with emphasis on Dothideomycetidae and Pleosporomycetidae. We accept three orders with 25 families and four orders with 94 families in Dothideomycetidae and Pleosporomycetidae, respectively. The new family Paralophiostomataceae is introduced in Pleosporales. Each family is provided with an updated description, notes, including figures to represent the morphology, list of accepted genera, and economic and ecological significances. We also provide an overall phylogenetic tree of families in Dothideomycetes based on combined analysis of LSU, SSU, rpb-2 and tefl sequence data, and phylogenetic trees for each order in Dothideomycetidae and Pleosporomycetidae. Family-level trees are provided for the families which include several genera such as Mycosphaerellaceae and Teratosphaeriaceae. Two new genera (Ligninsphaeriopsis and Paralophiostoma) are introduced. Five new species (Biatrisopora borsei, Comoclathris galatellae, Ligninsphaeriopsis thailandica, Paralophiostoma hysterioides and Torula thailandica) are introduced based on morphology and phylogeny, together with nine new reports and seven new collections from different families.
