Variably saturated flow conditions are increasingly relevant to geotechnical and hydrogeological assessments. This is most evident in the so-called vadose zone that extends from land surface to the phreatic surface, and which is characterised by variably saturated hydrological systems mostly at negative pore water pressures. The Vadose Zone: Hydrology of Variable Saturation in Engineering Geology and Hydrogeology short course explores this zone which is fundamental in understanding the subsurface component of the hydrological cycle, emphasising processes such as evapotranspiration, interflow, and groundwater recharge. Variable saturation provides special conditions whereby water not necessarily gravitates, and where aerobic or oxidising conditions can exist. This has important implications on groundwater recharge, vulnerability and susceptibility to contamination, as well as on the integrity of infrastructure and water management in the built environment.