Exposure is a well-known efficient therapeutic technique for anxiety disorders or irrational fear. The present article reviews the behavioral mechanisms of fear reduction in exposure-based therapies including simple exposure and systematic desensitization. The traditional and current theories of associative learning of Pavlovian conditioning, extinction, and response reemergence are applicable to acquisition, treatment, and relapse of fear. Despite recent transactions between basic animal research and human clinical studies on simple exposure therapy, little attention is paid to the counterconditioning process in systematic desensitization. By focusing on theoretical and experimental studies with animals and their implications for clinical settings, we propose further collaboration between basic and clinical studies.