Geomicrobiology is the scientific field at the intersection of geology and microbiology. It concerns the interactions of microorganisms with geological and geochemical processes, including the weathering and formation of rocks, minerals, soils and sediments and their influence on the hydrosphere. 

Geomicrobiology includes the study of extremophile organisms, microorganisms that thrive in environments normally considered hostile to life, extending to the origin of life on earth or other planets.

Understanding these limits of life are important in applied ecosystems, for example the microbial degradation of hydrocarbons associated with oil spills, in bioleaching - the use of microbes to extract metals from mine waste, and in mine site bioremediation.