Groundwater pollution is a global problem, impacting on the quality of life of people in both developed and developing countries. If we are to meet the ever-growing challenge to remediate these natural resources, then we need to look beyond the traditional methods of cleanup and embrace "alternative" technologies. One such technology is permeable reactive barriers (PRBs), which have had much success in the remediation of chlorinated solvent contaminated groundwaters and are now gaining recognition for the treatment of a range of other contaminants, both inorganic and organic.

This publication comprises a selection of peer-reviewed work presented at the first International Symposium on Permeable Reactive Barriers, held in Belfast, Northern Ireland in March 2004. This was the first international symposium of its kind focusing solely on this technology and providing researchers, industry and regulators with a platform from which to develop ideas and foster collaborations. Over 100 delegates attended the conference, representing both developed and developing countries, and attesting to the growing interest in this technology.

The papers focus on innovations in the field and the long-term performance of PRBs, and include the presentation of performance data from the first commercial granular iron barrier installed. I hope that after reading these contributions you will continue to support this technology and its many success stories.