The easily recognised genus Otidea is subjected to numerous problems in species identification. A numberof old names have undergone various interpretations, materials from different continents have not been compared andmisidentifications occur commonly. In this context, Otidea is monographed, based on our multiple gene phylogeniesassessing species boundaries and comparative morphological characters (see Hansen & Olariaga 2015). All namescombined in or synonymised with Otidea are dealt with. Thirty-three species are treated, with full descriptions andcolour illustrations provided for 25 of these. Five new species are described, viz. O. borealis, O. brunneoparva,O. oregonensis,O. pseudoleporina and O. subformicarum. Otidea cantharella var. minor and O. onotica var. brevisporaare elevated to species rank. Otideopsis kaushalii is combined in the genus Otidea. A key to the species of Otideais given. An LSU dataset containing 167 sequences (with 44 newly generated in this study) is analysed to placecollections and determine whether the named Otidea sequences in GenBank were identified correctly. Fourty-ninenew ITS sequences were generated in this study. The ITS region is too variable to align across Otidea, but had lowintraspecific variation and it aided in species identifications. Thirty type collections were studied, and ITS and LSUsequences are provided for 12 of these. A neotype is designated for O. cantharella and epitypes for O. concinna,O. leporina and O. onotica, along with several lectotypifications. The apothecial colour and shape, and spore charactersare important for species identification. We conclude that to distinguish closely related or morphologicallysimilar species, a combination of additional features are needed, i.e. the shape of the paraphyses, ectal excipulumstructure, types of ectal excipulum resinous exudates and their reactions in Melzer’s reagent and KOH, tomentumand basal mycelium colours and exudates. The KOH reaction of excipular resinous exudates and basal myceliumare introduced as novel taxonomic characters.