The permeable reactive barrier (PRB) is a relatively new technology that can be a cost-effective and low-maintenance remedy for a contaminated site. However, to use PRBs appropriately, the remedial manager must understand the technology, geological conditions of the site to be remediated, and the nature of the contaminants. The U.S. Environmental Protection Agency (USEPA) has sponsored research into PRBs, and the USEPA and several state regulatory agencies have approved PRB remedies at contaminated sites. This article succinctly presents the background of PRB technology, guides the new remedial manager through the process of determining if a PRB remedy is appropriate to for given site, discusses the pros and cons of PRBs, and outlines data requirements and guidelines of design for a PRB remedy. Summaries of existing sites with PRBs are given, along with a bibliography of government and environmental journal references.