I. Madison Bentley, also known as Isaac Madison Bentley and later as Madison Bentley (June 18, 1870 – May 29, 1955) was an American psychologist. His first publication in 1897 was under the name "I. Madison Bentley."

Bentley was one of the first to write about gender in his 1945 publication Sanity and Hazard in Childhood.

Isaac Madison Bentley was born in Clinton, Iowa to Charles Eugene Bentley and Persis Orilla Freeman on June 18, 1870.

The Bentleys were from Upstate New York, the town of Warners northeast of Syracuse.

Bentley studied psychology at the University of Nebraska. Harry Kirke Wolfe was his mentor. He also studied under Wilhelm Wundt at the University of Leipzig during the AY1886-1887, later taking his bachelor's degree in 1895. He then commenced graduate work at Cornell University under the supervision of Edward B. Titchener, receiving his PhD in 1899.

Isaac Madison Bentley was christened Isaac Madison, but abbreviated his first name to "I." sometime early in his adulthood. In 1909, he dropped the "I" because it was often misprinted as "J", especially in German publications.

Teaching at Cornell, Bentley was elevated to assistant professor in 1902; chairman of the Psychology Department in 1910. He left Cornell for Illinois in 1912. During the First World War, he conducted U.S. Army Air Corps research on the ear. In 1928, Bentley returned to Cornell and became Titchener's successor as the Sage Professor of Psychology and Chairman of the Psychology Department.

He died in Palo Alto, California on May 29, 1955, after a long illness.