On June 7-8, 1990, a Workshop attended by approximately 75 people was held in Cincinnati, Ohio, to present and discuss alternative barriers for liner and cover systems. Alternative barriers include thin, manufactured, low-permeability materials that are being used and being proposed for use in liner and cover systems for landfills, waste impoundments, site remediation projects, secondary containment structures, and other facilities. In some cases, the materials are being considered as an extra component of a liner or cover system, e.g., to back up a flexible membrane liner (FML), and in other cases the alternative barriers are being considered as a substitute for a thicker layer of compacted, low-permeability soil. The report contains a compilation of information available concerning alternative barrier materials and summarizes the main points brought out in the workshop. There are four main alternative barrier materials currently being produced. Three of them consist of a thin layer of bentonite sandwiched between two geotextiles, and the fourth consists of a thin layer of bentonite glued to an FML. All of the materials appear to have a very low hydraulic conductivity to water (between 1 x 10 to the 10th power cm/s and 1 x 10 to the 8th power cm/s, depending upon the conditions of testing). All of the materials are seamed in the field by overlapping sheets of the material and relying upon the bentonite to form its own seal when it hydrates. Data on the hydraulic integrity of the seams are much less complete compared to data on the materials themselves. The expansive nature of bentonite provides the bentonitic blankets with the capability of selfhealing small punctures, cracks, or other defects. The materials have many advantages, including fast installation with light-weight equipment. The most serious shortcomings are a lack of data, particularly on field performance, and the low shear strength of bentonite.