Summary “… do not take from me your laughter….. it opens for me all the doors of life” — Pablo NerudaBefore they speak or walk or crawl, infants joke. Infant laughter captured the attention of Aristotle, who thought it was the sign of the entry of the soul into the body, and of Darwin, who noted its emergence in the fourth month of life. Darwin saw such laughter as the early appreciation of humour, the presence at this age of which should not surprise us too much, given the early emergence of play in other mammals. In the twentieth century, however, these observations faded from scientific attention; humour began to be seen as an intellectual achievement requiring complex cognitive abilities, with infant laughter seen merely as a reaction to external stimuli. Recent research, however, has uncovered remarkable cognitive and emotional sensitivities in very young infants. And, as it turns out, humour and laughter in infants offer a rich source of insights into their understanding of the world, and indeed for our understanding of infants. The study of infant humour is no joke.