Dalton's Law of Partial Pressures, named after the English chemist John Dalton, is a fundamental principle in the study of gas mixtures. It states that in a mixture of non-reacting gases, the total pressure exerted by the mixture is equal to the sum of the partial pressures of each individual gas component.

According to this law, each gas in a mixture behaves independently and exerts its own pressure proportional to its concentration or mole fraction. The partial pressure of a gas can be defined as the pressure it would exert if it occupied the same volume alone under the same conditions of temperature and volume.