Most domestic dogs are completely weaned off of their mother's milk by the time they are 7 to 8 weeks old; larger breeds wean earlier. Weaning is a gradual process and begins at 3 to 4 weeks of age, when puppies begin to get their teeth.
Puppies do not wean all at once. They will continue to nurse, tapering off as the weeks go by. In the wild, adults in their pack would provide them with pre-chewed meat as they wean. In human households, puppies should be given wet food or dry kibble which has been moistened into a gruel. By the time they are completely weaned, puppies can consume dry food which has not been moistened.