AbstractUnlike most bird species, individual kingfisher species (Aves: Alcedinidae) are typically parasitized by only a single genus of louse (Alcedoffula,Alcedoecus, orEmersoniella). These louse genera are typically specific to a particular kingfisher subfamily. Specifically,AlcedoecusandEmersoniellaparasitize Halcyoninae, whereasAlcedoffulaparasitizes Alcedininae and Cerylinae. AlthoughEmersoniellais geographically restricted to the Indo-Pacific region,AlcedoecusandAlcedoffulaare geographically widespread. We used DNA sequences from two genes, the mitochondrial COI and nuclear EF-1αgenes, to infer phylogenies for the two geographically widespread genera of kingfisher lice,AlcedoffulaandAlcedoecus. These phylogenies included 47 kingfisher lice sampled from 11 of the 19 currently recognized genera of kingfishers. We compared louse phylogenies to host phylogenies to reconstruct their cophylogenetic history. Two distinct clades occur withinAlcedoffula, one that infests Alcedininae and a second that infests Cerylinae. All species ofAlcedoecuswere found only on host species of the subfamily Halcyoninae. Cophylogenetic analysis indicated thatAlcedoecus, as well as the clade ofAlcedoffulaoccurring on Alcedininae, do not show evidence of cospeciation. In contrast, the clade ofAlcedoffulaoccurring on Cerylinae showed strong evidence of cospeciation.