Removal of halogenated hydrocarbons from water by zero-valent iron is discussed. In situ processes based on filtration of groundwater through a permeable barrier formed by granular iron seem to be an advantageous alternative to traditional methods using, e.g., sorption or air stripping. However, only a few full-scale units for the decontamination of groundwater by the in situ "zero-valent" technology have been installed all over the world.