Prince William and his wife Kate's baby will be fifth in line to inherit the British throne, behind big brother Prince George and sister Princess Charlotte.
When the baby is born, everyone below will be moved down a place, including William's brother Prince Harry who will drop from fifth to sixth position.
The immediate line of succession to the throne includes Queen Elizabeth II's four children and their descendants:
1. PRINCE CHARLES, PRINCE OF WALES
-- Born 1948, eldest son of Queen Elizabeth
2. PRINCE WILLIAM, DUKE OF CAMBRIDGE
-- Born 1982, Charles's eldest son
3. PRINCE GEORGE OF CAMBRIDGE
-- Born 2013, William's son
4. PRINCESS CHARLOTTE OF CAMBRIDGE
-- Born 2015, William's daughter
5. BABY PRINCE OR PRINCESS OF CAMBRIDGE
-- Expected imminently, William's son or daughter
6. PRINCE HENRY OF WALES (PRINCE HARRY)
-- Born 1984, Charles' second son
7. PRINCE ANDREW, DUKE OF YORK
-- Born 1960, Queen Elizabeth's second son
8. PRINCESS BEATRICE OF YORK
-- Born 1988, Andrew's eldest daughter
9. PRINCESS EUGENIE OF YORK
-- Born 1990, Andrew's second daughter
10. PRINCE EDWARD, EARL OF WESSEX
-- Born 1964, Queen Elizabeth's third son
11. JAMES, VISCOUNT SEVERN
-- Born 2007, Edward's son
12. LADY LOUISE WINDSOR
-- Born 2003, Edward's daughter
13. PRINCESS ANNE, PRINCESS ROYAL
-- Born 1950, Queen Elizabeth's daughter
14. PETER PHILLIPS
-- Born 1977, Anne's son
15. SAVANNAH PHILLIPS
-- Born 2010, Phillips' eldest daughter
16. ISLA PHILLIPS
-- Born 2012, Phillips' second daughter
17. ZARA TINDALL
-- Born 1981, Anne's daughter
18. MIA TINDALL
-- Born 2014, Tindall's daughter
Queen Elizabeth's descendants are followed by those of her late sister princess Margaret, her only sibling.
The offspring of their father king George VI's siblings then follow. There are more than 60 living people descended from his father king George V, who died in 1936.
Only people descended from Sophia of Hanover can inherit the throne, according to the 1701 Act of Settlement.
The monarchy's website goes down as far as Zara Tindall, though some counts list more than 5,700 living descendants of Sophia, including Roman Catholics, who cannot inherit.
The highest excluded person is 26-year-old Edward Windsor, Lord Downpatrick, a first cousin twice removed of the queen, who converted to Catholicism. He would otherwise be 37th in line after the new baby is born.
In changes to the succession laws which came into effect in 2015, males born after October 28, 2011, no longer take precedence over their older sisters.
Also people married to Catholics are no longer excluded, with Downpatrick's father George Windsor, the Earl of St Andrews, the highest person restored to the line.
The line is a vast tangle of nobility and ordinary, untitled descendants from all corners of Europe. Several other European monarchs feature.
Besides Britain, it is also the line of succession to the thrones of 15 other Commonwealth realms.
