Jean Piaget proposed four stages of cognitive development that describe how children learn and think as they grow. The stages are: Sensorimotor (birth to 2 years), where infants learn through their senses and actions; Preoperational (2 to 7 years), characterized by symbolic thinking and egocentrism; Concrete Operational (7 to 11 years), where logical thinking develops but is limited to concrete objects; and Formal Operational (12 years and up), where abstract reasoning and problem-solving skills emerge. Each stage represents a different way of understanding the world, with children progressing through them in a fixed order. Piaget emphasized that children actively construct their knowledge through experiences, rather than passively absorbing information. This theory has influenced education and developmental psychology, highlighting the importance of age-appropriate learning activities.