Chromosomes of approximately 370 species of parasitic Hymenoptera (traditional Parasitica + Chrysidoidea) have been studied up to now. Arrhenotokous parthenogenesis is characteristic for the majority of parasitic wasps (thelytoky is less widespread there); females develop from diploid eggs, males - from haploid (rarely diploid) ones. Chromosomes of parasitic Hymenoptera are comparatively large (their average size is about 5-7 pm), each of them carries a single centromere. Chromosomes usually decrease in size more or less slowly within karyotypes, most of the chromosomes are biarmed, i.e. chromosome sets of parasitic wasps are comparatively symmetrical.Various parasitic Hymenoptera have haploid chromosome numbers of 2 to 21. The distribution of species by chromosome numbers is bimodal with the modes at n = 6 and 11. Centromeric and telomeric segments of the constitutive heterochromatin are the most frequent in karyotypes of parasitic wasps. Bivalents with one or two and more chiasmata are found in meiosis of parasitic wasps; bivalents with several chiasmata are more frequent in species with lower chromosome numbers. Following types of chromosomal mutations were found in parasitic wasps: deletions and duplications of the constitutive heterochromatin, inversions, translocations, centric and tandem fusions and fissions, polyploidy, aneuploidy, and numerical variation in B-chromosomes. Various types of chromosomal polymorphism were found in parasitic Hymenoptera, i.e. those in size of heterochromatic segments, translocations and number of B-chromosomes. Karyotypic rearrangements in parasitic wasps are asymmetrical in their mechanisms at the macroevolutionary level. During this process the decrease in chromosome numbers was possible due to chromosomal fusions (mostly tandem ones). In turn, the increase in chromosome numbers took place mainly due to the production of aneuploids and subsequent restoration of even chromosome numbers or (sufficiently less frequently) due to centric fissions accompanied by the tandem growth of the constitutive heterochromatin and the production of pseudoacrocentrics. The symmetrical karyotype with a relatively high chromosome number (n = 14-17) and the prevalence of biarmed chromosomes must be considered as a groundplan feature of parasitic wasps. An independent reduction of chromosome numbers took place in different lineages of parasitic Hymenoptera. Specifically, this reduction (from n = 14~17 down ton = 10~11 and less) took place in some lineages of the superfamily Ichneumonoidea (in the Ichneumonidae and Braconidae) as well as in the common ancestor of the Proctotrupoidea sensu lato, Cynipoidea and Chalcidoidea. Further multiple de-creases in chromosome numbers down to n = 4ù6 and less took place in various groups of the superfamily Chalcidoidea as well as in wasps of the family Dryinidae. Two main trends prevailed in the karyotype evolution of parasitic Hymenoptera: the reduction in chromosome numbers and (to a lesser extent) karyotypic dissymmetrization (due to an increase in size differentiation of chromosomes and in the share of acrocentrics in a chromosome set). An increase in chromosome numbers and in the degree of karyotypic symmetry also took place, although on a more restricted scale.Differences in chromosomal characters of parasitic Hymenoptera were found at various taxonomic levels: from superfamilies and families to morphologically indistinguishable populations. Use of karyotypic features for solving taxonomic problems in parasitic wasps is the most effective at the species level. About 15 groups of sibling species which differ in their chromosomal characters are known up to now. Specifically, karyotypic analysis has resulted in description of the two new species of the family Ichneumonidae, Aethecerus ranini and Tycherus australogeminus. It was found that Anisopteromalus calandrae (Pteromalidae), a well-known cosmopolitan parasite of various stored-product pests, appeared to be a complex of two closely related species differing in chromosome number (n = 5 and 7), some morphological characters, details of behaviour and life-history strategies. Significant differences in karyotypic characters were found in chalcidoids of the Nasonia species complex (Pteromalidae) and Aphelinus varipes s.l. (Aphelinidae). Morphologically identical populations with different chromosome numbers were found in the families Ichneumonidae (Ichneumon extensorius, I. suspiciosus) and Braconidae (Aphidius ervi, Charmon cruentatus). AI: Y BT: Systematics-; Documentation-; Publications-; Genetics-; Cytogenetics-; Chromosomes-; Evolution-; Parasites-diseases-and-disorders; Hosts-; Land-zones; Nearctic-region; Palaearctic-region Hymenoptera-: Comprehensive-works, Karyotypic-analysis-of-parasitic-taxa, Sex-determination-genetics, Karyotype-, Polymorphism-and-mutations, Mutation-, Karyotypic-mutations, Evolutionary-and-taxonomic-significance, Phylogeny-, Speciation-, Sibling-species, Karyotype-polymorphism-and-mutations-significance, Variation-, Karyotypic-polymorphism, Taxonomic-significance, Insect-hosts, Parasite-karyotype-polymorphism-and-mutations, monograph-, Eurasia-and-North-America, Eurasia-, North-America, Karyotype-polymorphism-and-mutations, phylogenetic-and-taxonomic-significance, parasitic-taxa ST: Hymenoptera- : Insecta- none2005