The objective of this study was to determine the state-of-the-art in underground, thin-seam mining systems, to identify new technology and procedures that would reduce the hazards in thin-seam mining, and to recommend areas for further research. The study was carried out in two phases, the first was devoted to a survey of authoritative literature. The practices adopted in various mining countries were analyzed and comparisons made to identify machines and methods with the potential for application in the United States. Published figures on U.S. bituminous coal reserves show the high proportion contained in thin seams and U.S. accident statistics demonstrate that the risk is greater in thin-seam operations. A comparison was made with the experiences of foreign operations. The second phase proceeded along two separate avenues to examine the distinctive problems associated with seam thicknesses above and below 30 inches. Current systems of mining appropriate to seams greater than 30 inches were elaborated and compared by a simulation exercise in terms of safety, production, and cost. For seams below 30 inches, less conventional systems, some presently disused, were studied and their potential evaluated; the research and development work necessary to make them viable are indicated.