Lice of the subgenus Dennyus (Collodennyus) are host specific, permanent parasites of swiftlets (Aves: Apodidae). As a prelude to a test of the hypothesis that these lice have cospeciated with their hosts, we revise the taxonomy of the subgenus, redescribing the seven previously recognized species, and adding thirteen new species and three new subspecies. All twenty-three of these louse taxa are found on swiftlets (Apodiformes: Apodidae), with four from hosts of the genus Collocalia, eighteen from Aerodramus, and one from Hydrochous. Successful identification is associated in most cases with females; males are only tenuously separable. A complete host–parasite list for the subgenus Collodennyus is provided, as well as a key for the identification of these taxa. Limited morphological variation within the subgenus has prevented ready extraction of discrete characters for cladistic analysis. In the absence of such characters, a cluster analysis of female and male lice is presented. Comparison of a dendrogram for Dennyus (Collodennyus) with a molecular phylogeny for the swiftlet hosts suggests that the history of the swiftlet–louse association has been complex, including episodes of host switching and independent speciation by the lice.