An estimated two billion viewers will be watching the wedding on TVs around the world.
The families are paying around 70 million quid for the shindig themselves but the Great British public are still forking out an estimated 20 million pounds for the security costs.
That pays for around 5,000 police officers, who will be helped by 35 dogs who are specially-trained to sniff for bombs. In a bid to make their job easier, the authorities have banned 60 convicted criminals from the area around Westminster Abbey as part of their bail terms.
1,900 guests have been invited to the ceremony, but only 600 will make it to lunch at the Palace. That gets whittled down to 300 for dinner and dancing.
There will be 187 horses on parade during the day. There'll be nine grey horses as part of the escort for the royal procession and five horse-drawn carriages.
Don't bother heading to John Lewis for the wedding list - the royal couple have instead chosen 26 charities to which guests and well-wishers can donate.
There are four bridesmaids for Kate - Eliza Lopes, Grace van Cutsem, The Hon. Margarita Armstrong-Jones and The Lady Louise Windsor. It's five if you include her Maid of Honour - younger sister Philippa Middleton
With all the talk of The Dress - Kate Middleton will actually sport three outfits. That wedding dress, plus a couple of other get-ups for the other parts of the day.
There'll be just one wedding ring though. Apparently Prince William - like his grandad Philip - won't be given a wedding band at the ceremony.
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