An intelligence quotient, or IQ, is a score derived from one of several different standardized tests designed to assess intelligence. The term "IQ" comes from the German Intelligenz-Quotient. When modern IQ tests are constructed the median score is set to 100 and a standard deviation to 15. Today almost all IQ tests adhere to the assignment of 15 IQ points to each standard deviation but this has not been the case historically. Approximately 95% of the population have scores within two standard deviations of the mean. If one SD is 15 points, then 95% of the population would be expected to have an IQ within a range of 70 to 130.

IQ scores have been shown to be associated with such factors as morbidity and mortality, parental social status and, to a substantial degree, parental IQ. While the heritability of IQ has been investigated for nearly a century, controversy remains regarding the significance of heritability estimates and the mechanisms of inheritance are still a matter of some debate.

IQ scores are used in many contexts: as predictors of educational achievement or special needs, by social scientists who study the distribution of IQ scores in populations and the relationships between Quick IQ Test score and other variables, and as predictors of job performance and income.

The average IQ scores for many populations have been rising at an average rate of three points per decade since the early 20th century, a phenomenon called the Flynn effect. It is disputed whether these changes in scores reflect real changes in intellectual abilities.