The term extensive aquifers is used to denote aquifers whose horizontal dimensions are much larger than their thicknesses, so that the losses of head due to the vertical velocity components may be neglected. The term groundwater hydraulics is used in the sense of deductive theory.   A series of strongly schematized problems is analysed with a view to applying the results in groundwater engineering. The publication is a text-book, not a manual, stress being laid on didactics, not on completeness or detail. The mathematical derivations are given in full, starting from the fundamental physical laws; mathematical methods, however, are not explained. As a rule, a problem is discussed in four stages: posing the problem, formulating the solution, deriving the formulae and analysing the result. The mathematical derivations are marked by a disjoined vertical line; they should be omitted at first reading, when the reader's attention should remain concentrated on the main issue of the theory. The basic laws and assumptions adopted are more or less consecrated by tradition. They have, however, a limited range of validity. This range has been established for some laws (e.g. the law of linear resistance). In other instances it forms the subject of modern investigations (e.g. the law relating the stored or released quantities of water to the rise or fall of the water table, where the notion of effective porosity is only an approximation). This physical side of the problem is not treated. It is thought too important to be discussed in complementary remarks to an essentially deductive study. If it were to be treated comprehensively, it should be made the subject of a separate study.   J.H. Edelman (1972) Groundwater hydraulics of extensive aquifers     ILRI publication 13, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, 216 pp.