This entry provides a definition of intelligence and reviews contemporary intelligence theories from an academic perspective. Intelligence is defined as the capacity to acquire new knowledge, apply abstract reasoning, and to adapt to the environment. Unitary and multi-trait theories of intelligence from Spearman’s g to Gardner’s Multiple Intelligences are reviewed. The Cattell-Horn-Carroll hierarchical perspective of intelligence is presented, followed by a review of Multiple Intelligences theory. Sternberg’s Triarchic theory of intelligence is also described. Last, a brief discussion of the relationship between performance on measures of intelligence and academic achievement in presented.