The different definitions of the term slate are specified, followed by a thorough explanation of the sedimentary patterns, mineralogy and fabric and their influence to the slate properties. Since not only slate in strict sense is used for roofing, the different and relevant fissile stone types are shortly introduced. Slate stands out from other stones due to its pronounced anisotropy, affecting more or less intensely all properties of the slate. The anisotropy is caused by the cleavage plane which is composed of mica layers and thus, highly depends on the mineralogical composition and the fabric of a slate. Both, mineralogy and the fabric govern the overall character of a slate and are therefore thoroughly explained. The rock-mechanical properties of slate are described, considering especially the dependence of the different strength values in respect to the orientation to the cleavage plane. The “finishing hardness” and the fissility especially in respect to the production are introduced. The chapter includes the physical properties of slate, comprising density and porosity, thermal conductivity and thermal expansion as well as the hydric and hygric behaviour. Furthermore, the optical parameter such as colours and the splitting surfaces of slates are described. The chapter includes various data from own investigations and from other published research to provide a comprehensive overview of the different slate properties and to enable the reader to work with it.