The scientific principle that states that every action has an equal and opposite reaction is known as Newton's Third Law of Motion. Formulated by Sir Isaac Newton, this principle indicates that for every force applied to an object, there is a corresponding force exerted in the opposite direction. This law is fundamental in the study of mechanics and helps explain various physical phenomena, including propulsion and collision interactions. Newton's Third Law has extensive applications in engineering, physics, and everyday situations, elucidating how forces operate in the physical world.