Development of treatment wall technology for the clean up of contaminated ground-water resources has expanded in the past few years. The main perceived advantage of this technology over ex situ and other in situ ground-water remediation approaches is reduced operation and maintenance costs. Since the first commercial application of zero-valent iron using a funnel-and-gate system for the removal of chlorinated hydrocarbons in February, 1995, several field-and pilot-scale studies are evaluating the feasibility of this technology for treatment of both organic and inorganic contaminants.Although, considerable design details have already been developed through fieldand pilot-scale applications of this technology, some critical issues (e.g., establishing tested and proven design procedures, improving construction technologies, documenting long-term performance, and evaluating synergy with other ground-water remediation technologies) still remain to be resolved. Currently planned field-scale tests and many ongoing laboratory studies are designed to address these issues and facilitate wider implementation of this technology.