The difference between classical and operant conditioning starts with the psychologist who discovered each technique, continues with the differences in behavior modification and how to elicit a desired outcome, and one focuses on involuntary behaviors while the other focuses on voluntary behaviors. Although both classical and operant conditioning result in learning through behavior modification, they are vastly different.
Classical conditioning was first described by Ivan Pavlov, a Russian physiologist who discovered he could modify an involuntary, automatic behavior by using a signal prior to a reflex. This was most notably demonstrated by Pavlov's famous experiment. He noted the dogs began to salivate after hearing a bell tone when the sound had been repeatedly paired with food. Even when food was not present, the dogs would salivate. He concluded that it was a learned response. Classical conditioning takes a previously neutral stimulus, such as the bell, and pairs it with an unconditioned stimulus, such as the taste of food, and uses them to condition a desired response, such as the salivation.
B.F. Skinner was the first psychologist to describe operant conditioning. It focuses on using either reinforcement or punishment to increase or decrease a behavior. This type of conditioning allows an association to form between the behavior and the consequences for that behavior. Animal trainers often use this form of conditioning during training. When the animal completes an action successfully, the trainer offers praise. If the animal does not perform the action requested, and then the trainer withholds the praise.