The generic name Polyborus has been traditionally associated with the “Crested Caracaras”, but confusion over its correct application has led to it recent falling out of use. Polyborus is based on a description by Marcgrave accompanied by a poor illustration, but only 2 species have ever been seriously considered as the identity of this description Long-winged Harrier Circus buffoni and Southern Caracara Caracara plancus. The nomenclatural history of this name is discussed and the identity of Marcgrave's description is elucidated as Yellow-headed Caracara Milvago chimachima. The implications for nomenclature are discussed, and it is recommended that both Polyborus and the name Falco brasiliensis (also based on the same description) be suppressed.