All its members are parasites in vertebrates when they are in their adult stage.

[1] It is accepted in the most recent classifications of the Nematoda,[2] in which it is one of the members of the order Trichocephalida.

However, Capillaria and closely related genera are sometimes included in the family Trichinellidae in other classifications.

The taxonomy of the Capillariidae is disputed: according to different classifications, the family includes the single genus Capillaria or 22 different genera (Amphibiocapillaria, Aonchotheca, Baruscapillaria, Calodium, Capillaria, Capillostrongyloides, Crocodylocapillaria, Echinocoleus, Eucoleus, Freitascapillaria, Gessyella, Liniscus, Paracapillaria, Paracapillaroides, Pearsonema, Paratrichosoma, Pseudocapillaria, Piscicapillaria, Pseudocapillaroides, Pterothominx, Schulmanela, and Tenoranema).

In contrast, certain species parasitic in fish, previously classified in Capillaria, are now considered members of the genus Huffmanela [3] (family Trichosomoididae).