Seven new species of the genus Aleiodes Wesmael, 1838 (Braconidae: Rogadinae) are described and illustrated: A. abraxanae sp. n., A. angustipterus sp. n., A. artesiariae sp. n., A. carminatus sp. n., A. diarsianae sp. n., A. leptofemur sp. n., and A. ryrholmi sp. n. A neotype is designated for each of Aleiodes circumscriptus (Nees, 1834) and A. pictus (Herrich-Schäffer, 1838), and both species are redescribed and illustrated. Aleiodes ochraceus Hellén, 1927 (not A. ochraceus (Curtis, 1834)) is renamed as A. curticornis nom. n. & stat. rev., and redescribed and illustrated. Aleiodes bistrigatus Roman, 1917, A. nigriceps Wesmael, 1838, and A. reticulatus (Noskiewicz, 1956), are re-instated as valid species. A lectotype is designated for Aleiodes bistrigatus Roman. An illustrated key is given to some distinctive species and the residual species groups along which further parts of an entire revision of western Palaearctic species of Aleiodes and Heterogamus will be organised. Biology, host associations and phenology are discussed for the keyed species (in addition to the above, A. albitibia (Herrich-Schäffer, 1838), A. apiculatus (Fahringer, 1932), A. arcticus (Thomson, 1892), A. cantherius (Lyle, 1919), A. esenbeckii (Hartig, 1834), A. jakowlewi (Kokujev, 1898), A. modestus (Reinhard, 1863), A. nigricornis Wesmael, 1838, A. pallidator (Thunberg, 1822), A. praetor (Reinhard, 1863), A. seriatus (Herrich- Schäffer, 1838) sensu lato, A. testaceus (Telenga, 1941), A. ungularis (Thomson, 1892), and A. varius (Herrich-Schäffer, 1838)) which are dealt with in full here (with the exception of A. seriatus s.l. which is, however, included in the key). The experimental methodology covering the revision as a whole, which involves some behavioural investigation, is outlined.