In situ characterization of the hydraulic properties of materials within the vadose zone has become increasingly important over the past several years, and is often the only viable means for testing certain geologic and engineered materials. A variety of field methods exist for the hydraulic characterization of unsaturated materials, including ring-type infiltrometers, air and gas permeameters, air-entry permeameters, borehole permeameters, disc permeameters, sorptivity tubes, infiltration ponds, crust tests, and drainage-type instantaneous profile tests. These methods provide information on a number of hydraulic properties, including soil infiltration rate, permeability to air and soil gas, saturated and unsaturated hydraulic conductivity, sorptivity, mean pore size, and matric flux potential. A wide range of materials may be tested in the field, including sandy alluvium, natural clay and engineered clay liners and barriers, fractured and unfractured rock, and soils with macropores. Each of the available tests is appropriate for different geologic materials and testing requirements. The favorable results of a number of these applications demonstrate that most of these methods are reliable, useful, and economical for characterization of unsaturated materials within the vadose zone.