This book provides the state of the art of the investigation and the in-depth analysis of hydraulic  conductivity from the theoretical to semi-empirical models to policy development associated with management of land resources emanating from drainageproblem soils. Many international experts   contributed to the development of this book. It is envisaged that this thought provoking book of international repute will excite and appeal to academics, researchers and university students who seek to explore the breadth and in-depth knowledge about hydraulic conductivity. Investigations into hydraulic conductivity is important to the understanding of the movement of solutes and water in the terrestrial environment and/or the hydrosphere-biosphere interface. Transport of these fl uids has various implications on the ecology and quality of environment and subsequently sustenance of livelihoods of the increasing world population. In particular, water fl ow in the vadose zone is of fundamental importance to geoscientists, soil scientists, hydrogeologists and hydrologists and is a critical element in assessing environmental implications of soil management. For example, free water at the soil-atmosphere interface is a source of great importance to man. Effi cient management of this water will require greater control of hydraulic conductivity in order to solve such wide ranging problems as upland fl ooding, pollution of surface and ground-waters, and ineffi cient irrigation of agricultural lands. It is generally recognized that progress of science depends increasingly on an advanced understanding diff erences in the methods of investigations and their applicability to solving real problems in the ecological fragile environment. In this book a number of approaches were employed in assessing hydraulic conductivity including theoretically and quasi-semi empirical models and conclude with applied policy considerations. Of particular importance is the analysis of hydraulic conductivity at the macro-scale to pore scale i.e theoretical conceptions from the geological structures (rock pore space) to broken rock mass or saprolite (soil-microscopic level) in order to  understand the transport phenomena in underground aquifers and porous media in soils. Water fl ow and solute transport through soil are directly related to the geometry of the available pore space. The role of macroporosity in groundwater movement cannot be overemphasized, for example, recharging the  groundwater by the rapid movement of water through soil macropores may aff ect simultaneous movement of undesirable constituents and resultant rapid contamination of the subsurface water resources. This has accentuated the need to come up with robust modeling approaches to analyzing the hydraulic conductivity. For instance, in the last two decades, models have been explored in the fi eld of soil physics to study fl ow processes at the pore scale. While the measurements of hydraulic conductivity is usually tedious and a diff  cult, it is imperative that diff erent approaches be employed to derive or predict and accurately estimate hydraulic conductivity. For this reason, the book is covered in 4 sections including: Part 1- Mechanistic and Geotechnical Modelling Approaches; Part 2-Empirical Modeling Approaches to Estimating Hydraulic Conductivity; Part 3- Laboratory Hydraulic Conductivity Measurements and Part 4- Implications of Hydraulic Conductivity on Land Management and Policy Development. Part 1 explores the robust mechanical and geotechnical theoretical methods to analyse hydraulic conductivity and includes topics such as i) Infl uence of degree of saturation in the electric resistivity-hydraulic conductivity relationship, ii) Stress/strain-dependent properties of hydraulic conductivity for fractured rocks and Hydraulic conductivity and water retention curve of highly comprehensible materials iii). On the other hand part 2 covers in-depth analysis of the empirical models to estimating hydraulic conductivity and covered salient topic features including i) Correlations between hydraulic conductivity and selected hydrogeological properties of rocks, ii) Hydraulic Conductivity of layered anisotropic media, and iii) Rock mass hydraulic conductivity estimated by two empirical models. Use of measuring techniques and deterministic laboratory hydraulic conductivity measurements are covered in part 3 and includes topics such as i) Unsaturated hydraulic conductivity for evaporation in heterogeneous soils ii) Determination of hydraulic conductivity of undisturbed soil column: A measurement accomplished with the Gamma Ray Transmission Technique and iii) Hydraulic conductivity of semiquasi stable soils: Eff ects of particulate mobility. Part 4 concludes the book with some applications of hydraulic conductivity implications on land management and policy development and covers interesting topics such as i) Saturated hydraulic conductivity and land use change, new insights to the payments for ecosystem services programs: a case study from a tropical montane cloud forest watershed in eastern central Mexico and ii) Hydraulic conductivity and landfi ll construction. In conclusion, this book is structured in a way as to overview the state of the art analyses of hydraulic conductivity and I hope it will serve the interests of the stakeholders involved in the applications of science of transport of water and solutes to understanding the dynamics of fl uids fl ow in porous media. In particular the development of policies and strategies pertinent to water availability and management is critical to the improved livelihoods of the nations of the world.