A baby koala is referred to as a joey and is hairless, blind, and earless. At birth the joey, only 20 mm (0.79 in) long, crawls into the downward-facing pouch on the mother's belly (which is closed by a drawstring-like muscle that the mother can tighten at will) and attaches itself to one of the two teats.

Young remain hidden in the pouch for about six months, feeding on only milk. During this time they grow ears, eyes, and fur. After six months the joey then begins to explore outside of the pouch. At about this stage it begins to consume small quantities of the mother’s "pap" (formerly thought to be excrement, but now thought to come from the mother's cecum) in order to inoculate its gut with the microbes necessary to digest eucalypt leaves.^[1] The joey will remain with its mother for another six months or so, riding on her back, and feeding on both milk and eucalyptus leaves until weaning is complete at about 12 months of age.