This chapter introduces tailings as fine-grained waste by-products originated usually from the milling process. Tailings characteristics vary with the type of minerals involved as well as the flow sheets of the milling process. Both the physical and chemical characteristics of tailings influence the selection and detail design of an optimal tailings storage facility. As the amount of tailings generated in a modern mine is enormous, therefore whenever appropriate, the use of tailings material itself to construct its storage facility makes good economical sense.