This article reviews findings on the predictive validity of psychometric tests of intelligence. The article is divided into five major parts. In the first part, the issues with which the article deals are introduced. In the second part, we discuss what psychologists can learn about the predictive validity of intelligence tests from results obtained in the established market economies. Intelligence quotient (IQ) is considered in relation to educational achievement, employment prospects and wealth generation, career outcomes, and well-being. In the third part, the intelligence tests (primarily for infants and children) that yield the IQ scores are discussed. In the fourth part, constraints are presented on the interpretations of findings, including cross-cultural issues. We conclude that conventional tests of intelligence can be useful but only if they are interpreted very carefully, taking into account the factors that can affect them, and in conjunction with other measures.