The term phytoremediation was coined in the 1980s to describe the use of plants to ameliorate degraded or polluted substrates. Utilizing plants to control soil and water degradation has a long history. Many early agriculturalists developed plant-based systems to minimize soil erosion, and the use of plants to restore disturbed environments and cleanse water is well established. In the 20th century, the potential of plants as extractors of pollutants began to be explored, for example during investigations of radionuclide-contaminated soils by Nishita and colleagues in the 1950s. In the last decade or so there has been rapid development of scientific methods relevant to phytoremediation. It is, therefore, an appropriate time to consider methodological developments in phytoremediation and to review their current use. In Parts I and II of Phytoremediation: Methods and Reviews, methods are described for enhancing contaminant degradation, uptake, and tolerance by plants, for exploiting plant biodiversity for phytoremediation, for modifying contaminant availability, and for experimentally analyzing phytoremediation potential. Then, in Parts III and IV, a variety of phytoremediation technologies and their use around the world is reviewed.