The child, who will be the third in line to the British throne, is due July 13 and could arrive any day.
Media have already staked out positions with duct tape and stepladders near St. Mary's Hospital to try to get a glimpse of the royal baby the minute he or she arrives.
The new parents are expected to disappear from the public eye as they build a life far more private than that of William's parents.
The royal pair has decided to keep the sex of the baby a surprise, but either way, the baby will still be the heir. A recent change in British parliamentary rules will allow the baby to be the monarch regardless of sex.
The first announcement from the palace will come when Kate is admitted into the hospital, where she will deliver in the same suite that Princess Diana gave birth to Kate's husband.
The formal birth announcement will follow shortly thereafter on a traditional paper announcement hung outside Buckingham Palace.
The London Mint announced that a "lucky silver penny" will be given to British babies born the same day as the royal baby.
People worldwide have already started to buy in to royal baby mania, and Britain is expected to net more than $400 million in sales of the souvenirs.