A key to the genera of Scelionidae of the Holarctic region is given. Sixty-seven genera are recognized in three subfamilies, viz. Telenominae, Teleasinae, and Scelioninae. Seven new genera and six new species are described from America north of Mexico, viz. Aradoctonus armatus n. gen. and n. sp. (Telenominae, Telenomini), Embioctonus setiger n. gen. and n. sp. (Scelioninae, Embidobiini), Epigryon audax n. gen. and n. sp. (Scelioninae, Gryonini), Exon californicum n. gen. and n. sp. (Scelioninae, Gryonini), Harringtonia n. gen. for Baryconus cinctus Harrington (Scelioninae, Psilanteridini), Mecix texana n. gen. and n. sp. (Scelioninae, Psilanteridini), and Spiniteleia campbelli n. gen. and n. sp. (Scelioninae, Psilanteridini). The Nearctic and Palearctic faunas of Scelionidae are compared, analyzed, and tabulated on generic level. Twenty-eight plates with 207 scanning electron micrographs and line drawings are included.