The first public announcement that the birth is imminent will be made once Kate is in hospital and in the early stages of labour.
When the baby is born, Kate's parents and the Queen will be told before a statement is issued.
A formal declaration will then be driven to Buckingham Palace and placed on an easel. The same happened after Prince William's birth.
The public will be told the baby's gender, weight, and time of birth but it may be some time before William and Kate decide on a name.