In economics, marginal utility is the extra satisfaction gained from consuming one more unit of a good.
The concept helps explain why consumers often value successive units less than earlier ones. For example, the first glass of water may be extremely valuable to a thirsty person, while a fourth glass adds much less satisfaction. This pattern is called diminishing marginal utility.
The idea became central to the marginalist revolution of the 1870s, associated with William Stanley Jevons, Carl Menger, and Léon Walras. Their work shifted economic analysis toward choices made at the margin rather than only toward total quantities.
Marginal utility is not the same as total utility, which is the satisfaction from all units consumed. It is also distinct from consumer surplus, which measures the difference between what a buyer is willing to pay and what they actually pay. In modern economics, utility is usually treated as a model of preferences rather than a directly measurable physical quantity.