This volume of Studies in Mycology is dedicated to Amy Y. Rossman, who published fundamental papers revising numerous genera and species in the Hypocreales. This title contains five contributions treating fungi in the families Hypocreaceae and Nectriaceae in the order Hypocreales. The plant pathogenic genus Calonectria represents a serious threat to the growth and sustainability of plantation forestry of Eucalyptus in both Brazil and Southeastern China. Both contributions treating Calonectria in this issue highlight the high species diversity in relatively small areas surveyed. A total of 38 novel Calonectria spp. (20 from Brazil and 18 from China) are introduced associated with a single genus, which in itself is very surprising. In Colombia, isolations from various Pinus species in plantations and nurseries displaying pitch canker disease symptoms resulted in the identification of more than 10 novel Fusarium species, five of which were provided with names. Pathogenicity results showed that two of the novel Fusarium taxa described, displayed levels of pathogenicity comparable to F. circinatum, therefore posing a new risk to commercial Pinus forestry in Colombia and other parts of the world. The genus Trichoderma is treated based on a large-scale survey of plant and fungal material conducted in Southern Europe and Macaronesia. A morphological and phylogenetic study allowed for the recognition of more than 90 species, of which 17 are newly described. Furthermore, Aphysiostroma stercorarium is combined in Trichoderma and a genus-wide phylogeny based on fragments of the RNA polymerase II subunit B and larger subunit of ATP citrate lyase gene regions are presented. The ascomycete family Nectriaceae includes numerous important plant and human pathogens, as well as several species used extensively in industrial and commercial applications. To address the poorly defined generic and species concepts in this family, a robust phylogenetic study using 10 loci was conducted for available type and authentic strains of genera known in Nectriaceae. For several of these genera, no sequence data were previously available, and therefore this contribution represents the largest sampling of nectriaceous fungi subjected to multi-locus sequence analyses to date. Forty-seven genera, of which six are new, and one new family, Tilachlidiaceae, were resolved. Additionally, several genera were proposed for synonymy based on the abolishment of dual nomenclature. This contribution provides a broad phylogenetic backbone and framework for future studies of the Nectriaceae.