Some Encyrtids parasites of Psyllids have been specially studied and the species of four genera are mentioned here. 1) The genusTrechnitesThomson, of whichPsylledontusCrawford is a new synonym, withTr. psyllae (Ruschka), redescribed from Versailles, France, as a parasite ofPsylla pyri. The American speciesTr. (Psylledontus) insidiosusCrawford is considered as a distinct species. 2) The genusPrionomitusMayr, with the well known speciesPr. mitratusDalm., parasites ofPsylla pyri andPs. pyrisuga, of which a large number has been bred in Versailles. Specimens, males and females, bred fromPsylla peregrina, differ fromPr. mitratus and are identified asPr. tiliarisDalm. 3) In the genusPsyllaephagusAshmead, three new species are described,Ps. pistaciae from Iran and Turkey,Ps. agonoscemae from South of France andPs. merceti from Spain, a redescription is given ofPs. femoralisBorelli and a key of the palearctic species has been prepared. 4) Other specimens bred in Versailles fromPsylla pyri belong to the genusAphidencyrtusAshmead and are being described under the name ofAph. cantabricusMercet.