Slate is one of the most permanent roofing materials available. It was quarried as early as the second quarter of the eighteenth century in Pennsylvania and Maryland. Its prominence grew as it became an important component of fashionable structures during the Victorian period. Although it requires little maintenance, when failures occur they usually originate in flashings, attachment nails, faults in original installation, and damage from external sources and not in the stone. The physical properties, the production process and historical uses of slate are covered in this article that also gives information on slate selection, weight considerations, exposure, and jointing, and attachment flashing. Two case studies are discussed in detail: The Oswego City Hall in Oswego, New York (1869 structure with a three color slate mansard roof), and the Otsego County Courthouse in Cooperstown, New York (1880 Colonial Revival structure). -- AATA