Feather mites (Astigmata: Analgoidea, Pterolichoidea) are among the most abundant and commonly occurring bird ectosymbionts. Basic questions on the ecology and evolution of feather mites remain unanswered because feather mite species identification is often only possible for adult males and it is laborious even for specialised taxonomists, thus precluding large-scale identifications. Here, DNA barcoding was tested as a useful molecular tool to identify feather mites from passerine birds. 361 specimens of 72 species of feather mites from 68 species of European passerine birds from Russia and Spain were barcoded. The accuracy of barcoding and mini-barcoding was tested. Moreover, threshold choice (a controversial issue in barcoding studies) was also explored in a new way, by calculating through simulations the effect of sampling effort (in species number and species composition) on threshold calculations. One 200 bp mini-barcode region showed the same accuracy as the full-length barcode (602 bp) and was surrounded by conserved regions potentially useful for group-specific degenerate primers. Species identification accuracy was perfect (100%) but decreased when singletons or species of the Proctophyllodes pinnatus group were included. In fact, barcoding confirmed previous taxonomic issues within the Proctophyllodes pinnatus group. Following an integrative taxonomy approach, authors compared the barcode study with previous taxonomic knowledge on feather mites, discovering three new putative cryptic species and validating three previous morphologically different (but still undescribed) new species. informacion[at]ebd.csic.es Doña et al (2015) DNA barcoding and mini-barcoding as a powerful tool for feather mite studies Mol Ecol Res DOI: 10.1111/1755-0998.12384