Geochemistry is the study of the development, and distribution of chemical elements on Earth, which are found in rock-forming minerals and their byproducts, as well as in living beings, water, and the environment. The elemental geochemical variation of sediments is used to recognize the mechanisms controlling the estuarine environment and serves as a baseline for assessing the environmental effect in the future. Geochemistry is a unique field that deals with the study of mineral deposits. It also addresses the interconnections between the structures of rock, soil, water, and air, which vary according to different places. Furthermore, groundwater is the solely accessible water supply in many desert basins, particularly in developing nations. Geochemical indicators are proper instruments for addressing a diversity of hydrological issues, particularly in arid and semi-arid settings. Thermodynamically, the fugacity of oxygen (fO2) in solid earth varies by many orders of magnitude. Enstatite chondrites can have high levels of hydrogen abundance, hydrogen, and nitrogen isotope compositions like those of the earth’s mantle. The chapter deals with the basic concept of geochemistry and its types, as well as the development of geochemistry. It also explains elemental and isotopes geochemistry, human health, and medical geochemistry.