The study of Peruvian cichlids presented here covers about 20% of the known South American cichlid species, a group which has not been revised in its entirety since the cursory revision 80 years ago by Regan (1905-1906). This paper is based on personal field work and review of most museum collections of Peruvian cichlids, encompassing a total of well over 4000 specimens. Its principal aim is to serve as a basic treatise on the taxonomy and distribution of the western Amazonian cichlids, including also an analysis of distribution patterns in that area.