Which of Newton's laws states that for every action there is an equal and opposite reaction?

Newton's third law of motion states that for every action there is an equal and opposite reaction — when one object exerts a force on a second, the second exerts an equal force in the opposite direction on the first. A rocket pushing exhaust down and being pushed up is a classic example. Newton's first law is the law of inertia (objects keep their motion unless acted on by a force); the second law relates force, mass, and acceleration (F = ma). Knowing all three laws and an example of each is common General Science content.