Piagetian theory is a foundational framework in developmental psychology that describes the nature and development of human intelligence. It investigates the stages and processes by which individuals construct knowledge and understanding of the world, characterized by distinct, sequential cognitive stages (sensorimotor, preoperational, concrete operational, formal operational) and mechanisms of adaptation such as assimilation and accommodation. Its significance lies in providing a comprehensive model for understanding cognitive evolution, profoundly influencing research and practice in child development and education.