Introduction.-The main types of groundwater base-levels -- Factors controlling base- level elevation changes -- General -- Global, regional and local climate changes -- Tectonic movements -- Isostatic and glacio- isostatic movements -- Land subsidence through compaction and dewatering -- Groundwater cones of depression caused by natural process of evapotranspiration -- Groundwater cones of depression caused by groundwater exploitation -- Methods and techniques to define base-level elevation and to measure and assess -- The effect of their variation on adjoining groundwater systems -- Base level elevation -- Current ground level measurements -- Current sea and lake level measurements -- Paleo- and historic shorelines -- Methods to determine groundwater systems' response to base- level changes -- Current field measurements -- Indirect estimation -- Hydrological simulations -- Capturing of groundwater basins and shifts of divides -- General -- Climate changes -- Tectonically induced base-level elevation changes -- Karst systems -- Stream piracy by groundwater sapping -- Groundwater exploitation -- Salinity, salination, and freshening of the different base-levels and their adjoining groundwater systems -- General -- The global marine base-level -- Base- level salinity -- Adjoining groundwater systems salinity -- Continental endorheic base-levels, distant from the sea -- Base-level salinity -- Adjoining groundwater systems salinity -- Flow- through, intermediate, base-levels -- Base-level salinity.-Adjoining groundwater systems salinity -- Salinity of endorheic base-levels below sea level, close to the sea -- Freshening of coastal aquifers -- Paleo- and current marine base-levels -- General -- The Neogene marine Mediterranean base-level -- The Black Sea Neogene to Holocene base-levels.-Quaternary and Holocene marine base-levels -- Current marine base-levels -- Characteristics of current continental endorheic base-levels -- Current continental base-levels above sea level -- General -- Lake Chad Basin -- The Great Salt Lake Basin -- The Andean Altiplano Basin -- The Aral Sea Basin -- The Mono Lake Basin, California -- The Main Ethiopian Rift Basin -- Current continental base-levels below sea level and distant from the sea -- General -- The Great Artesian Basin and Lake Eyre Basin, Australia -- The Death Valley Basin -- Central Asia closed endorheic basins -- The Caspian Sea -Kara Bogaz Gol Basin -- Current continental base-levels below sea level, located close to the sea -- General -- The Dead Sea Rift endorheic base-level -- General -- Structure and tectonics -- The hydrological history of the Dead Sea Rift endorheic base-level -- Current groundwater flow regime -- Water salinities of the Dead Sea Rift base-levels and their adjoining groundwater systems -- The response of the groundwater systems to the Dead Sea base-level changes -- The Afar Depression-Lake Asal -- The Qattara Depression, Egypt -- The Salton Trough, USA -- The Chotts of Tunisia and Algeria -- The Sabkhat Ghuzayil and the Sirte Basin, Libya -- The Lago Enriquillo, Dominican Republic -- The Argentine Salinas close to the Atlantic coast -- Sebkha Paki Tah Depression, Morocco -- Salination mechanism -- Anowledgements -- Subject Index. The proposed book deals with the role of changing groundwater base level on the adjacent hydrological systems. It summarizes, compiles and compares results of current and paleo base levels, using examples from all over the world. A classification is given for marine or continental groundwater base levels with special attention to those below sea level. The factors controlling base level changes and the methods for their determination are elaborated. Holocene and future changes are discussed with their effect on salinization and flushing mechanisms of groundwater. All topics described in the book are accompanied by examples and references from all over the world.