Extinction is the weakening and eventual disappearance of a conditioned response when the conditioned stimulus is repeatedly presented without the unconditioned stimulus, or when a reinforced behavior is no longer reinforced.

In classical conditioning, a tone that once predicted food loses its power to elicit salivation if food no longer follows. In operant conditioning, a lever-press that once produced pellets gradually declines when the pellets stop. Extinction is not the same as forgetting or unlearning; the original association often remains latent. Spontaneous recovery can occur after a rest period, and relearning is usually faster than original acquisition.

Extinction is the basis of exposure therapies for anxiety disorders. By confronting the feared stimulus without the expected negative outcome, the patient learns a new safety association that competes with the old fear. The process requires careful management; incomplete extinction or return of the original context can reinstate the response.

Extinction teaches that a once-reliable predictor is no longer reliable. The behavior adjusts accordingly.