The paper will give a general overview/problem definition and state-of-the-art of the natural processes of biodegradation and chemical transformations. The importance and problems of delivery and recovery systems will be emphasized. In-situ treatment technologies will be classified into extraction processes (air stripping, flushing, freezing, electrokinetics, vegetative and thermal) and immobilization and degradation processes (grouting, fixation, thermal fusion, chemical and biological). Documented case histories of an in-situ treatment at several sites will be presented. This will include some of the ongoing and completed EPA/ORD activities.