Neonectria is a cosmopolitan genus and it is, in part, defined by its link to the anamorph genus Cylindrocarpon. Neonectria has been divided into informal groups on the basis of combined morphology of anamorph and teleomorph. Previously, Cylindrocarpon was divided into four groups defined by presence or absence of microconidia and chlamydospores. Molecular phylogenetic analyses have indicated that Neonectria sensu stricto and Cylindrocarpon sensu stricto are phylogenetically congeneric. In addition, morphological and molecular data accumulated over several years have indicated that Neonectria sensu lato and Cylindrocarpon sensu lato do not form a monophyletic group and that the respective informal groups may represent distinct genera. In the present work, a multilocus analysis (act, ITS, LSU, rpb1, tef1, tub) was applied to representatives of the informal groups to determine their level of phylogenetic support as a first step towards taxonomic revision of Neonectria sensu lato. Results show five distinct highly supported clades that correspond to some extent with the informal Neonectria and Cylindrocarpon groups that are here recognised as genera: (1) N. coccineagroup and Cylindrocarpon groups 1 & 4 (Neonectria/Cylindrocarpon sensu stricto); (2) N. rugulosa-group (Rugonectria gen. nov.); (3) N. mammoidea/N. veuillotiana-groups and Cylindrocarpon group 2 (Thelonectria gen. nov.); (4) N. radicicola-group and Cylindrocarpon group 3 (Ilyonectria gen. nov.); and (5) anamorph genus Campylocarpon. Characteristics of the anamorphs and teleomorphs correlate with the five genera, three of which are newly described. New combinations are made for species where their classification is confirmed by phylogenetic data. Key words: Canker-causing fungi, molecular systematics, Nectria-like fungi, phylogeny, polyphasic taxonomy, root- rotting fungi, sequence analysis, systematics, taxonomy. Taxonomic novelties: Ilyonectria P. Chaverri & C. Salgado, gen. nov.; Ilyonectria coprosmae (Dingley) P. Chaverri & C. Salgado, comb. nov.; Ilyonectria liriodendri (Halleen et al.) P. Chaverri & C. Salgado, comb. nov.; Ilyonectria macrodydima (Halleen, Schroers & Crous) P. Chaverri & C. Salgado, comb. nov.; Ilyonectria radicicola (Gerlach & L. Nilsoon) P. Chaverri & C. Salgado, comb. nov.; Rugonectria P. Chaverri & Samuels, gen. nov.; Rugonectria castaneicola (W. Yamam. & Oyasu) Hirooka & P. Chaverri, comb. nov; Rugonectria neobalansae (Samuels) P. Chaverri & Samuels, comb. nov.; Rugonectria rugulosa (Pat. & Gaill.) Samuels, P. Chaverri & C. Salgado, comb. nov.; Thelonectria P. Chaverri & C. Salgado, gen. nov.; Thelonectria coronata (Penz. & Sacc.) P. Chaverri & C. Salgado, comb. nov.; Thelonectria discophora (Mont.) P. Chaverri & C. Salgado, comb. nov.; Thelonectriajungneri(Henn.) P. Chaverri & C. Salgado, comb. nov.; Thelonectria lucida (Hohnel) P. Chaverri & C. Salgado, comb. nov.; Thelonectria olida (Wollenw.) P. Chaverri & C. Salgado, comb. nov; Thelonectria trachosa (Samuels & Brayford) Samuels, P. Chaverri & C. Salgado, comb. nov.; Thelonectria veuillotiana (Sacc. & Roum.) P. Chaverri & C. Salgado, comb. nov.; Thelonectria viridispora (Samuels & Brayford) P. Chaverri, C. Salgado, & Samuels, comb. nov.; Thelonectria westlandica (Dingley) P. Chaverri & C. Salgado, comb. nov.