This first part of a two-part commentary examines evidence for the notion that human milk production is at least in part controlled by the infant's appetite. The studies that we review, of milk production by breastfeeding and expressing mothers, strongly support this hypothesis. Therefore, in established lactation and with a demand feeding regime, a mother's milk production is likely to be a reflection of her infant's appetite, rather than her ability to produce milk, which may in fact be several-fold higher. However, previous studies of human milk production have not provided a clear insight into how the lactating breast matches milk production to infant demand.