Fundamental concepts of Unsaturated Soil Mechanics are being increasingly applied in the practice of geotechnics worldwide. The unique materials documented in this book stem from renewed momentum in a longstanding search for testing methodologies that are most suitable for modelling the engineering response of unsaturated soils, as the excitement in this area is providing more reliable analytical tools and yielding ever safer and more sustainable design guidelines. The book outlines recent advances in experimental modelling of unsaturated geomaterials, particularly cohesive-frictional soils, such as silty sand, clayey silty sand, sandy silt, and silty clay, over a wide range of stress paths and modes of deformation. Experimental techniques include suction-controlled resonant column, bender element, biaxial (plane strain), triaxial, true triaxial, and ring shear testing, via either axis-translation or vapour-pressure technique. The chapters cover main testing procedures, key experimental results, and calibration protocols for constitutive modelling of these materials over a relatively large range of matric and/or total suction states (0 - 300 MPa).