Intelligence Quotient (IQ) is a numerical measure designed to estimate an individual's cognitive abilities in relation to others of the same age group. In cognitive psychology, IQ is considered an important indicator of intellectual functioning, reflecting capacities such as reasoning, problem-solving, abstract thinking, learning, comprehension, and adaptation to new situations. The concept originated from the need to assess mental abilities systematically and has become one of the most widely used measures in educational, clinical, and occupational settings. The history of IQ began with Alfred Binet and Théodore Simon in the early twentieth century, who developed the first intelligence test to identify school children requiring special educational support. They introduced the idea of mental age, referring to the level of intellectual performance expected for a particular chronological age. Later, William Stern proposed the Intelligence Quotient formula: IQ = (Mental Age ÷ Chronological Age) × 100. Although modern intelligence tests no longer use this formula, the term IQ has remained in use. Contemporary tests calculate IQ based on an