The Flynn effect is the substantial and long-sustained increase in both fluid and crystallized intelligence test scores that were measured in many parts of the world over the 20th century, named after researcher James Flynn (1934–2020). When intelligence quotient (IQ) tests are initially standardized using a sample of test-takers, by convention the average of the test results is set to 100 and their standard deviation is set to 15 or 16 IQ points. When IQ tests are revised, they are again standardized using a new sample of test-takers, usually born more recently than the first; the average result is set to 100. When the new test subjects take the older tests, in almost every case their average scores are significantly above 100.

James Robert Flynn was an American-born New Zealand moral philosopher and intelligence researcher. Originally from Washington, D.C., and educated at the University of Chicago, Flynn emigrated to Dunedin in 1963, where he taught political studies at the University of Otago. He was noted for his publications about the continued year-after-year increase of IQ scores throughout the world, which is now referred to as the Flynn effect. In addition to his academic work, he championed social democratic politics throughout his life.