Remediation of subsurface contamination is an up-to-date subject, due to the high number of contaminated sites in all developed countries. Risk assessment for long term exposure to humans is the approach most applied world-wide to identify contaminated sites and the remediation target limits. Exposure pathways for humans at polluted sited often involve inhalation of vapours from soil or groundwater, both outdoor and within enclosed spaces. Many models are available for this purpose, based on concentration input data referred to different media (soil gas, soil, groundwater) located below the ground surface or buildings. This book discusses research in this field in order to improve both modelling tools and field measurements.