Main hydrogeological subdivisions are the aquifers complexes and horizons differentiated according to different criteria. The purpose of present research is assessment of characteristics of the main aquifer complexes and horizons in the limits of the Republic of Moldova. The data sources used for present research are the State Fund on Subsoil Information, laboratory investigations, cartographic and bibliographic sources on the groundwater monitoring data. Short description of aquifers complexes and horizons is provided below. The Holocenic Aquifer (аА3) is characterized by the presence of sands, often with gravel inclusions. The thicknesses of the rocks is 20-30 m. The flow of the wells is equal to 1-2 l/sec. The aquifer rocks of the Pontian horizon (N2р) are granular sands. Their depth varies from 2-40 m to 5-120 m to the southwest, and the groundwater depth - from 1-5 m to 50-90 m. The Upper Sarmatian-Meotian aquifer (N1S3-m) is formed from fine-grained sands, siltstone with intercalation of clays. The thickness of the aquifer rocks varies from 20.0 m to 300 m (in the south part). The Middle Sarmatian aquifer (Congerian) (N1S2) comprises the congerian sands of the Middle Sarmatian. Rocks are fine-grained sands with intercalation of clay, sandstone and limestone. The aquifer horizon thickness ranges from 5-15 m to 20-30 m. The Badenian-Sarmatian aquifer (N1b-s) is developed everywhere. The aquifer rocks are the reef limestone, with intercalation of marls and sands. The thickness is 30-50 m, in some areas increasing up to 100-500 m. The hydrogeological conditions of the country are determined by the geological structure of the territory, the tectonic conditions, the anthropogenic, climatological, geomorphological factors, through which aquifer structures with a high degree of complexity have been generated.