A standardized test is a test that is administered and scored in a consistent or standard manner. Standardized tests are designed in such a way that the questions and interpretations are consistent and are administered and scored in a predetermined, standard manner.

A standardized test is administered and scored uniformly for all test takers. Any test in which the same test is given in the same manner to all test takers, and graded in the same manner for everyone, is a standardized test. Standardized tests do not need to be high-stakes tests, time-limited tests, multiple-choice tests, academic tests, or tests given to large numbers of test takers. Standardized tests can take various forms, including written, oral, or practical test. The standardized test may evaluate many subjects, including driving, creativity, athleticism, personality, professional ethics, as well as academic skills.

The opposite of standardized testing is non-standardized testing, in which either significantly different tests are given to different test takers, or the same test is assigned under significantly different conditions or evaluated differently.

Most everyday quizzes and tests taken by students during school meet the definition of a standardized test: everyone in the class takes the same test, at the same time, under the same circumstances, and all of the tests are graded by their teacher in the same way. However, the term standardized test is most commonly used to refer to tests that are given to larger groups, such as a test taken by all adults who wish to acquire a license to get a particular job, or by all students of a certain age. Most standardized tests are summative assessments (assessments that measure the learning of the participants at the end of an instructional unit).

Because everyone gets the same test and the same grading system, standardized tests are often perceived as being fairer than non-standardized tests. Such tests are often thought of as more objective than a system in which some test takers get an easier test and others get a more difficult test. Standardized tests are designed to permit reliable comparison of outcomes across all test takers because everyone is taking the same test and being graded the same way.

The definition of a standardized test has changed somewhat over time. In 1960, standardized tests were defined as those in which the conditions and content were equal for everyone taking the test, regardless of when, where, or by whom the test was given or graded. Standardized tests have a consistent, uniform method for scoring. This means that all test takers who answer a test question in the same way will get the same score for that question. The purpose of this standardization is to make sure that the scores reliably indicate the abilities or skills being measured, and not other variables.

By the beginning of the 21st century, the focus shifted away from a strict sameness of conditions towards equal fairness of testing conditions. For example, a test taker with a broken wrist might write more slowly because of the injury, and it would be more equitable, and produce a more reliable understanding of the test taker's actual knowledge, if that person were given a few more minutes to write down the answers to a time-limited test. Changing the testing conditions in a way that improves fairness with respect to a permanent or temporary disability, but without undermining the main point of the assessment, is called an accommodation.  However, if the accommodation undermines the purpose of the test, then the allowances would become a modification of the content, and no longer a standardized test.

The earliest evidence of standardized testing was in China, during the Han dynasty, where the imperial examinations covered the Six Arts which included music, archery, horsemanship, arithmetic, writing, and knowledge of the rituals and ceremonies of both public and private parts. These exams were used to select employees for the state bureaucracy.