Ivan Petrovich Pavlov (September 26 [O.S. 14 September] 1849 – February 27 , 1936) is a Russian physiologist known primarily for his work in classical conditioning.

From his childhood days Pavlov has demonstrated intellectual curiosity along with an unusual energy which he refers to as "the instinct for research".

Inspired by the progressive ideas which D. I. Pisarev, the most eminent of the Russian literary critics of the 1860s, and I. M. Sechenov, the father of Russian physiology, are spreading, Pavlov abandons his religious career and devotes his life to science.

In 1870, he enrolls in the physics and mathematics department at the University of Saint Petersburg in order to study natural science.

Pavlov wins the Nobel Prize for Physiology or Medicine in 1904, becoming the first Russian Nobel laureate.

A survey in the Review of General Psychology, published in 2002, will rank Pavlov as the twenty-fourth most cited psychologist of the twentieth century.

Pavlov's principles of classical conditioning will be found to operate across a variety of behavior therapies and in experimental and clinical settings, such as educational classrooms and even reducing phobias with systematic desensitization.