We examine Jean Piaget’s theory of cognitive development, which outlines four stages: Sensorimotor, Preoperational, Concrete Operational, and Formal Operational. Each stage represents different ways children think, learn, and grow, from understanding the world through senses and actions in infancy to developing abstract and logical thinking in adolescence. Piaget’s theory has significantly influenced educational practices, emphasizing active learning, developmentally appropriate activities, and the constructivist approach. Despite criticisms about underestimating children's abilities and cultural biases, Piaget’s work remains foundational in developmental psychology.