Originally published in English in 1976, the book draws on and extends our knowledge of the process of learning. The subject of the study is the general stage in a child's development that comes between his successful performance of an activity without knowing how he did it - that is, what he had to do in order to succeed - and the times when he becomes aware of what went into that action. The book reports the results of experiments conducted at the Centre of Genetic Epistemology. Children, ranging in age between four and adolescence, were asked to perform such tasks as walking on all fours, playing tiddlywinks, building a ramp for a toy car. They were then asked to explain how they had performed the task, and in some cases, to instruct the interviewer. Their answers show a number of surprising inaccuracies in the child's ability to grasp the nature of what he has done.

Taking a broad view of his results, Piaget shows that they reveal several stages in the gradual development of the child's conceptualization of his actions. In analysing each stage, Piaget argues that the child's concept of his own action cannot be considered a simple matter of 'enlightenment', but must actively be reconstructed from his experience. This view has always been at the core of Piaget's work, and a new area of the child's mental world is here given definitive treatment.