Positive feedback is a process that occurs in a feedback loop in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation.

That is, A produces more of B which in turn produces more of A.

In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback.

Both concepts play an important role in science and engineering, including biology, chemistry, and cybernetics.