The host rocks are sedimentary rocks that include quartzites, slates, older cherty carbonate and iron formations. There are three types of host rocks, namely, crystalline rocks, clay rocks and salt rocks. In the context of radioactive ore deposits, safe enclosure of the host rocks is affected by technical, geo-technical and geological barriers. In the context of mining, majority of mining wastes are connected to the acquisition of host rock along with other processes that result in the production of metals including copper, aluminum, gold and iron, or nonmetals like gravel, asbestos, coal, gypsum, etc. Host rocks in the vicinity of hydrothermal mineral deposits frequently exchange elements with hydrothermal fluids and thus lead to the formation of alteration minerals. The density and volume of the host rock is affected by mineralogical alterations. This book is a compilation of chapters that discuss the most vital concepts on the geology and geochemistry of host rocks. It will provide comprehensive knowledge to the readers.