Hymenopteran insects, including bees, ants and wasps, play an essential role in agricultural production, ecological maintenance, and pest management. The symbiotic microbiomes of these and other insects are essential guardians of host health and fitness. This paper reviews the most recent progress in research on symbiotic microbiomes of the Symphyta, Aculeata (Apoidea, Formicide and Vespoidea) and Parasitica (parasitic wasps), and their transmission routes in hymenopterans. We also discuss the relationships between the microbiome and host’s developmental stage, season, diet, caste and geographic location. Furthermore, we introduce the role of symbiotic microbiomes in host food digestion, nutrient provision, metabolic detoxication, reproductive manipulation, resistance to pathogens and parasites and behavioral modulation. Prospects for sustainable agricultural and forestry development, and pharmaceutical research are discussed, and a vision for the future is outlined.