The ACT (pronounced as an initialism, /ˌeɪˌsiːˈtiː/ ay-see-tee; originally abbreviation of American College Testing) is a standardized test for high school achievement and college admissions in the US produced by ACT, Inc. It was first administered in November 1959 by Everett Franklin Lindquist as a competitor to the College Board's Scholastic Aptitude Test, now the SAT Reasoning Test.

The ACT test has historically consisted of four tests: English, Mathematics, Reading, and Science Reasoning. In February 2005, an optional Writing test was added to the ACT, mirroring changes to the SAT that took place later in March of the same year. All 4-year colleges and universities in the U.S. accept the ACT, but different institutions place different emphases on standardized tests such as the ACT, compared to other factors of evaluation such as class rank, G.P.A., and extracurricular activities.

The main four tests are scored individually on a scale of 1-36, and a Composite score is provided which is the whole number average of the four scores. In 2005 the company established ACT International. 

This organization is composed of ACT Education Solutions, Limited, and ACT Business Solutions, B.V. ACT Education Solutions is directed toward helping non-native speakers learn English in preparation for studying at an English-speaking educational institution. ACT Business Solutions attempts to help employers assess their employees' level of English proficiency through use of the WorkKeys assessment.