Groundwater is a crucial source of fresh water for domestic, agricultural and industrial uses, and for maintaining aquaticand groundwater-dependent ecosystems. It is also of importance for identifying and securing sustainable use of energy resources and subsurface storage sites. Groundwater interacts with different parts of system earth, including the atmosphere, surface water, soil, geological environment and with many geological processes. This chapter provides an overview of groundwater systems in the Netherlands and the Dutch continental shelf at depths from the surface down to about 5 km. The overview shows how the groundwater systems are shaped by the interplay between natural mechanisms operating on various geological timescales and the impact of anthropogenic activities. Important mechanisms involved in the development of groundwater flow systems include differences in the elevation of the groundwater table (its topographic relief), contrasts in groundwater density and hydromechanical interaction of groundwater with geologic media. The topography-driven groundwater flow systems in the coastal dunes, Pleistocene ice-pushed ridges, and the southeastern part of the country contain important fresh groundwater resources of meteoric origin. These resources occur largely in unconsolidated sedimentary sequences of Holocene and Pleistocene to Neogene age. Natural and anthropogenic factors explain the Holocene history of salinization and seepage in the coastal zone. The large transboundary topography-driven groundwater flow system in the southeast of the Netherlands has developed since Miocene times. It induced freshening of groundwater to relatively great depths and cooling of subsurface temperatures. Case studies show the effects of shallow and deep fault zones on flow and chemical conditions of groundwater. Groundwater in older, pre-Paleogene to Carboniferous units outside the realm of topography-driven flow mostly consists of highly saline brines. Groundwater in these units also shows high overpressures in the northern offshore and northern and northeastern part of the Netherlands, while close to hydrostatic pressures prevail in the southern onshore and adjacent offshore area.This spatial difference reflects the differences in burial history and hydrogeological framework.