The phylogenetic relationships of the aquiline eagles are incompletely known, but two recent studies based on DNA sequence data both place Harpia near the base of this radiation (Helbig et al. 2005, Haring et al. 2007).
Schulenberg, T. S. (2009). Harpy Eagle (Harpia harpyja), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.hareag1.01