Abraham Flexner (November 13, 1866 – September 21, 1959) was an American educator, best known for his role in the 20th century reform of medical and higher education in the United States and Canada.

After founding and directing a college-preparatory school in his hometown of Louisville, Kentucky, Flexner published a critical assessment of the state of the American educational system in 1908 titled The American College: A Criticism. His work attracted the Carnegie Foundation to commission an in-depth evaluation into 155 medical schools in the US and Canada. It was his resultant self-titled Flexner Report, published in 1910, that sparked the reform of medical education in the United States and Canada. Flexner was also a founder of the Institute for Advanced Study in Princeton, which brought together some of the greatest minds in history to collaborate on intellectual discovery and research.

Flexner was born in Louisville, Kentucky on November 13, 1866. He was the sixth of nine children born to German Jewish immigrants Ester and Moritz Flexner. He was the first in his family to complete high school and go on to college. In 1886, at age 19, Flexner completed a B.A. in classics at Johns Hopkins University, where he studied for only two years. In 1905, he pursued graduate studies in psychology at Harvard University, and at the University of Berlin. He did not, however, complete work on an advanced degree at either institution.

Flexner had three brothers named Jacob, Bernard and Simon Flexner. He also had a sister named Rachel Flexner.

The success of Abraham Flexner's experimental schooling allowed him to help finance Simon Flexner's medical education at Johns Hopkins School of Medicine. He proceeded to become a pathologist, bacteriologist and a medical researcher employed by the Rockefeller Institute for Medical Research from 1901 to 1935.

Flexner also financed his sister's undergraduate studies at Bryn Mawr College. Jacob ran a drugstore and used the profits from selling the establishment to attend medical school. He then practiced as a physician in Louisville. Bernard pursued a career in law and later practiced in both Chicago and New York.

In 1896, Flexner married a former student of his school, Anne Laziere Crawford. She was a teacher who soon became a successful playwright and children's author. The success of her play Mrs. Wiggs of the Cabbage Patch (based on the 1901 novel) funded Flexner's studies at Harvard and his year abroad at European universities. The couple supported women's suffrage and had two daughters Jean and Eleanor. Jean went on to become one of the original employees of the United States Division of Labor Standards. Eleanor Flexner became an independent scholar and pioneer of women's studies.

Flexner grew up in an Orthodox Jewish family; however, early on he became a religious agnostic.