Reservoir engineering is the academic and applied discipline focused on the study, characterization, modeling, and management of subsurface reservoirs containing fluids such as hydrocarbons, water, or geothermal energy. This field integrates principles from geology, physics, chemistry, and mathematics to analyze reservoir properties and fluid behavior, predict performance under various production and injection scenarios, and optimize strategies for resource extraction, recovery, and sustainable management, often employing numerical simulation techniques. Its significance lies in enabling the efficient and economic development and stewardship of these critical subsurface resources.