Traditionally, this order comprises only a single family, Falconidae (falcons, carcaras). More recently, however, it has been suggested to recognise two families, Falconidae and Herpetotheridae. 

References

Fuchs, J., J.A. Johnson, and D.P. Mindell (2012), Molecular systematics of the caracaras and allies (Falconidae: Polyborinae) inferred from mitochondrial and

nuclear sequence data, Ibis 154, 520-532. (abstract)

Fuchs, J., J.A. Johnson, and D.P. Mindell (2015), Rapid diversification of falcons (Aves: Falconidae) due to expansion of open habitats in the Late Miocene,

Mol. Phylogenet. Evol. 82, 166-182. (abstract)

Griffiths, C.S., G.F. Barrowclough, J.G. Groth and L.A. Mertz (2004), Phylogeny of the Falconidae (Aves): a comparison of the efficacy of morphological,

mitochondrial, and nuclear data, Mol. Phylogenet. Evol. 32, 101-109. (abstract)

Liu, G., L. Zhou, and G. Zhao (2019), Complete mitochondrial genomes of five raptors and implications for the phylogenetic relationships between owls and

nightjars, PeerJ Preprints, publ: 12 Jan 2019. DOI: 10.7287/peerj.preprints.27478v1. (pdf)

Mindell, D.P., J. Fuchs, and J.A. Johnson (2018), Phylogeny, taxonomy, and geographic diversity of diurnal raptors: Falconiformes, Accipitriformes, and

Cathartiformes, In: Sarasola, J.H. et al., Birds of prey, Chapter 1, 3-32. Springer.  (abstract)

Oswald, J.A., J.M. Allen, K.E. Witt, R.A. Folk, N.A. Albury, D.W. Steadman, and R.P. Guralnick (2019), Ancient DNA from a 2,500-year-old Caribbean fossil

places an extinct bird (Caracara creightoni) in a phylogenetic context, Mol. Phylogenet. Evol. 140:106576. DOI: 10.1016/j.ympev.2019.106576.
 (abstract)