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Robert Sessions Woodworth (1869-1962) was an influential American academic psychologist of the first half of the twentieth century. His textbook Psychology: A study of mental life, which appeared first in 1921, went through many editions and was the first introduction to psychology for generations of undergraduate students. His 1938 textbook of Experimental Psychology was scarcely less influential, especially in the 1954 2nd edition, written with Harold H. Schlosberg.

In the 1929 second edition of the earlier text, Woodworth introduced the expression Stimulus-Organism-Response (S-O-R) to describe his functionalist approach to psychology and to stress its difference from the strictly Stimulus-Response (S-R) approach of the behaviorists.

During World War One, Woodworth created the Woodworth Personal Data Survey (WPDS), which has been called the first personality test. The WPDS was designed to identify new recruits who were likely to suffer "shell shock" while fighting overseas. Although the test was designed too late for it to be used operationally, the test was highly influential in the development of later personality inventories.