Robert Sessions Woodworth (1869-1962) was an influential American academic psychologist of the first half of the twentieth century. He studied under William James along with such prominent psychologists as Leta Stetter Hollingworth, James Rowland Angell, and Edward Thorndike. A graduate of Harvard and Columbia, 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 second edition, written with Harold H. Schlosberg. He is known for introducing the Stimulus-Organism-Response (S-O-R) formula of behavior.