The application of microwave energy in areas other than food preparation has become a major research effort worldwide. Although not new, this energy source has recently shown promise in areas such as selectively heating minerals and ores to aid in crushing, and in processing advanced ceramics to improve their reliability along with reducing manufacturing costs. The heating effect of microwave energy on materials is dependent on several factors, such as the magnitude of the electric field, the frequency of the field, the thermal properties, and the dielectric properties of the material. The U.S. Bureau of Mines Tuscaloosa Research Center has been involved in a research program since 1984 to investigate the dielectric properties of materials. The purpose of this research effort was to fill the void in literature on dielectric property data at microwave heating frequencies. With an understanding of the dielectric properties of materials, researchers and engineers can readily explore the usefulness of microwaves as a potentially viable energy source for industrial applications.