Crowds are gathering in central London for the wedding of Prince William and Kate Middleton at Westminster Abbey.
Thousands of people have camped out overnight on the procession route that the couple will take to Buckingham Palace.
The weather forecasts reckon the day will start off dry but they say in London there's a risk of heavy showers.
Watch Newsround's coverage on CBBC throughout the day, and check out the Newsround website for updates.
BBC reporters think there are 3,000-5,000 who camped in London overnight and they're expecting 600,000 people on the streets by the time of the service.
And it's not just about London. There are a whopping 5,500 street parties are taking place - including one hosted by Prime Minister David Cameron at Downing Street.
And Larry the Downing Street cat has made an effort too.