The proper identification of fleas forms a sound basis for disease prevention and flea control. This publication, prepared primarily as a taxonomic revision, will help those called upon to identify the species of these insects and recommend control procedures. Full descriptions are given of the genera ad higher groups, accompanied in most instances by figures. For species, subspecies, and varieties formal descriptions are avoided, but data have usually been supplied for each as follows: Indication of synonymy, name of type host, type locality, statement relative to range, and remarks upon identification characteristics, nature of original description, references to figures, published notes on biology or economic importance, and redescriptions.