This is a compendium of current knowledge about the crustacean subclass Branchiura Thorell, 1864. An overview of the group is presented, starting from the first species description, and reports of taxonomic changes. It also provides a condensed retrospect of each genus and includes the characteristics of each genus, the geographical distribution of each species arranged according to occurrence per continent; and aspects of the anatomy, physiology, host-parasite interactions and phylogeny are discussed. In order to condense the information available on members of the subclass, additional literature sources on each aspect are tabulated. This text will be useful for fish health practitioners, researchers and students of Parasitology and Fish Veterinary Medicine. The contents of this volume were originally published in 2016 in Crustaceana volume 89, issue 11-12.