Behaviorism is a set of learning theories and approaches concerned with the behavior, as opposed to mental states, of human and non-human animals. In psychology, it seeks to explain behavior through external physical stimuli, responses, reinforcements, and learning histories.
Behaviorism's objective and experimental methods significantly contributed to psychology's legitimacy in the sciences; for decades, the approach dominated experimental psychology.
Russian scientist Ivan Pavlov (1849-1936)'s research on classical conditioning (or stimulus-response) significantly influenced the early days of behaviorism. According to Pavlov, conditioned reflexes are learning behaviors in which animals or humans are made to produce reflex (unconscious) responses to an initial stimulus and then conditioned to perform the reflex response to a second stimulus associated with the original stimulus over time.
Pavlov famously worked with salivation in response to the presence of food. In addition to the initial food stimulus, a second stimulus, such as a specific sound, could be used to evoke the salivation reflex (the desired response). Once the response to the second stimulus had been "learned," the food stimulus was no longer required to induce salivation.
The study of behaviorists' learning processes goes beyond Pavlov's "classical conditioning."