A lithotroph is a type of microorganism that derives its energy for growth and survival from the oxidation of inorganic compounds, as opposed to organotrophs, which obtain their energy from organic compounds. The term "lithotroph" is derived from the Greek words "lithos" (rock) and "troph" (eater), literally meaning "rock eater." Lithotrophs are important components of various environmental ecosystems, playing a crucial role in biogeochemical cycles, such as the nitrogen cycle and the sulfur cycle.

There are different types of lithotrophs, each utilizing different inorganic substances for energy. For example, some oxidize ferrous iron to ferric iron, others use sulfur compounds or hydrogen gas, and still others are able to use ammonia or nitrite in their metabolic processes. These organisms are found in a variety of habitats, often in extreme environments where organic compounds are scarce, such as deep ocean vents, hot springs, and mineral-rich soils. Their ability to utilize inorganic substances makes them key players in the cycling of nutrients and in the maintenance of ecosystem stability.