Hydrogeological models (HM) are being developed in order to gain information that is needed for management of groundwater resources protection and sustainable consumption. Specialists of Riga Technical university (RTU) have developed two regional scales HM of Latvia: in 1993-1996, REMO (Large Riga) and, in 2010-2012, LAMO1 (the first HM version). REMO covered the central part of Latvia and its plane approximation step was 4000 meters. LAMO1 encloses the ground territory of Latvia, the Gulf of Riga, and border areas with neighboring countries (Estonia, Lithuania, Russian Federation, Belorussia). The HM plane step is 500 meters. Presently, the neighboring areas of HM are not active. In the case of a transboundary projects the neighboring country must provide hydrogeological data necessary to activate its neighboring area. LAMO1 generalizes geological and hydrogeological data that have been accumulated by the Latvian Environment, geology and Meteorology Centre (LEGMC). LAMO runs into the environment of licensed software Groundwater Vistas that is being used worldwide for modelling groundwater processes. In 2012-2015, LAMO1 has been considerably updated, in order to improve quality of results provided by HM. The LAMO2 version (2013) accounted for deep river valleys cutting the primary strata; the thick Devonian D2ar aquifer was replaced by the two aquifers and the aquitard that separated them; due to this innovation, the number of the HM planes increased from 25 to 27. In 2014, the LAMO3 version was obtained by increasing density of the HM hydrogeological network (number of rivers and lakes, increased, accordingly, from 199 to 469 and from 67 to 127). For the current LAMO4 version, the plane step was reduced from 500 to 250 meters; the groundwater inflow for rivers was calibrated by accounting for information obtained from measurements of river flows. For LAMO1 and LAMO2, the permeability of primary aquifers (k maps) was modelled by using a constant permeability value for an aquifer. In LAMO3 and LAMO4, the more realistic k maps were obtained by accounting for pumping data of wells. Presently, the latest LAMO4 version is being used by LEGMC and RTU specialists as the source of information on the geometry and permeability of geological strata, on distributions of groundwater heads and flows, on interaction between groundwater and surface water bodies (sea, lakes, rivers, precipitation). LAMO4 has been used by RTU as a tool for investigating nature processes of the groundwater system of Latvia. The first results were quite unexpected, because it was found out that the river watershed basin concept could not be used for the deepest strata of the basin. Research on LAMO3 and LAMO4 is supported by the Latvian state research program EVIDEnT. Keywords Hydrogeological model, hydrographical network, groundwater heads, groundwater flow balance, geological section.