The ACT (; originally an abbreviation of American College Testing) is a standardized test used for college admissions in the United States. It is currently administered by ACT, a nonprofit organization of the same name. The ACT test covers four academic skill areas: English, mathematics, reading, and scientific reasoning. It also offers an optional direct writing test. It is accepted by all four-year colleges and universities in the United States as well as more than 225 universities outside of the U.S.

The main four ACT test sections are individually scored on a scale of 1–36, and a composite score (the rounded whole number average of the four sections) is provided.

The ACT was first introduced in November 1959 by University of Iowa professor Everett Franklin Lindquist as a competitor to the Scholastic Aptitude Test (SAT). The ACT originally consisted of four tests: English, Mathematics, Social Studies, and Natural Sciences. In 1989, however, the Social Studies test was changed into a Reading section (which included a social sciences subsection), and the Natural Sciences test was renamed the Science Reasoning test, with more emphasis on problem-solving skills as opposed to memorizing scientific facts. In February 2005, an optional Writing Test was added to the ACT. By the fall of 2017, computer-based ACT tests were available for school-day testing in limited school districts of the US, with greater availability expected in fall of 2018.

The ACT has seen a gradual increase in the number of test takers since its inception, and in 2012 the ACT surpassed the SAT for the first time in total test takers; that year, 1,666,017 students took the ACT and 1,664,479 students took the SAT.