Demarcation of family, genus and species boundaries in the Diaporthales has been tentative due to uninformative illustrations and descriptions, overlapping morphological characteristics, misplacement or poor condition of type specimens and shortage of molecular data from ex-type cultures. In this study, we obtained the type specimens or other authentic specimens of diaporthalean taxa from worldwide fungaria. We examined, described and illustrated them. This study is based on morphological characters from type or authentic specimens, details from protologue and original illustrations and molecular data obtained from GenBank. Combined analyses of nrITS, nrLSU, RPB2 and TEF1- sequence data were used to construct the molecular phylogeny. Additionally, we provided separate phylogenetic trees for families when necessary to show the generic distribution within these families based on suitable gene markers. Based on morphology and phylogeny, we treat 17 genera previously assigned to Diaporthales genera incertae sedis within several families. For some genera we have designated new generic types as they are lacking type species or type species have affiliations with other families. We exclude Anisomycopsis from Diaporthales and place it in Xylariomycetidae genera incertae sedis. Tirisporellaceae, which was previously placed in Tirisporellales is placed in Diaporthales based on phylogeny and morphology. A new combination, Dendrostoma leiphaemia propose for Amphiporthe leiphaemia (Fr.) Butin. Based on the morphological characters and molecular data we accept 27 families and 138 genera within Diaporthales, 24 genera in Diaporthales genera incertae sedis and one genus in Xylariomycetidae genera incertae sedis. We provide notes for genera in Diaporthales genera incertae sedis, and excluded and doubtful genera are listed with notes on their taxonomy and phylogeny.