Permeable reactive barriers (PRBs) employ an innovative technology that offers a passive system for addressing long-term groundwater (GW) contamination problems. This chapter reviews the design and construction technologies for PRB, with particular emphasis on their application for remediation of chlorinated hydrocarbon (CHC)-contaminated GW. It aims to identify key issues that need to be addressed to increase the performance and longevity of PRB systems. While the chapter focuses on CHC and the use of zero-valent iron, the parameters optimized for the design of PRBs are the same irrespective of the contaminant and material used as the reactive barrier. A detailed knowledge of the site hydrogeology (e.g., an understanding of aquifer and aquitard), geochemistry (e.g., GW chemistry other than for the chemical of concern), and chemistry of contaminants (e.g., source, composition, and concentrations) is required for successful PRB design. The reactive vessel PRB design is very similar to the funnel-and-gate barrier except that it replaces the gate with in situ reactive vessels.