This synthesis will be of interest to administrators and policy makers; pavement, material, geotechnical, and environmental engineers; and maintenance and construction professionals involved with highway design and construction issues. Information is provided on the technical, economic, and environmental aspects (including legislative and regulatory considerations) of recycling and using waste materials and by-products in highway construction. The quantities, characteristics, possible uses, current and past research activities, and actual highway construction use of each waste material or by-product is provided. This information, based on a review of nearly 1,000 references and on responses to a 1991 survey (updated in 1993), is classified into four broad categories based on source: agricultural, domestic, industrial, and mineral wastes. A Technical Appendix to this document containing an extensive bibliography, supporting information, and details regarding the use of selected waste materials and by-products is available separately from the Transportation Research Board.