Intelligence is one of the most influential yet contested constructs in psychology. Psychometric research, beginning with early intelligence testing and the proposal of a general factor of intelligence, established influential models that continue to shape scientific and applied work. Yet competing theories, challenging the focus on abstract reasoning, highlight ongoing disputes about the nature of intelligence and the assessment of intellectual differences among individuals. Central debates concern the relationship between measurement and theory and the ontological status of the g factor—particularly whether intelligence is reducible to neurocognitive processes or must be treated as an emergent phenomenon. Contemporary research is marked by ontological and epistemological pluralism, reflecting divergent explanatory aims and practical needs. This pluralism also carries normative implications, as different conceptions of intelligence guide educational practices, inform policy, and shape broader societal understandings of human cognitive abilities.