Biogeochemistry is a relatively new interdisciplinary field exploring the link between biotic and abiotic constituents. It investigates physical, chemical, geological, and biological reactions and processes that govern the biogeochemical cycles essential to sustain life on earth. Geosphere and biosphere are the two major components of the earth that play an imperative role in biogeochemical cycles, involving the transformation and fluxes of chemical elements and nutrients among different parts of the ecosystem. The geosphere on earth is around 4.54 billion years, and various indigenous and exogenous processes have resulted in the formation and evolution of the biosphere over 3.5 billion years. During the past few years, anthropogenic activities have significantly contributed to the biogeochemical processes, causing a cascade of changes to the earth's ecosystem. The current chapter focuses on important aspects of biogeochemistry concerning the geosphere, biosphere, natural and artificial biogeochemical cycles, different areas of biogeochemistry, and applications of biogeochemistry.