The feather mite family Eustathiidae Oudemans is a presumably monophyletic group of ectoparasites restricted to swifts & crested swifts (Apodiformes: Apodidae & Hemiprocnidae). The mites occur in tandem between the barbs of the primary regimes of the wings of field-collected birds & museum skins. Discrete spatial relations exist between the pop¿s. of different mite species when these co-occur on an individual bird. The secondaries, tertiaries, coverts, & retrices of the tail provide loci of infestations in such instances. This study establishes a classification & describes the morphology & host-parasite assoc. of the Eustathiidae. All taxa are (re)described, keys are provided for the determination of genera & species, & host-parasite assoc. are cross-listed. Illus.