Millions of TV viewers will be tuning in to watch the royal wedding live on TV. Here's an armchair guide to what to expect:
Live coverage of the day's events by the BBC will be presented by Kirsty Young, Huw Edwards and Dermot O'Leary among others.
Julie Etchingham and Phillip Schofield will lead ITV's coverage.
Sky News is screening the proceedings in ultra high definition with Kay Burley presenting from a special studio on the Long Walk.
0900: Members of the public who have been invited to watch the wedding day from the grounds of Windsor Castle begin to arrive.
0930: Wedding guests begin arriving at the castle's famous Round Tower by coach. They will enter St George's Chapel through the South Door and take their seats.
1120: Members of the Royal Family begin arriving, entering via the Galilee Porch, some on foot and others by car.
Around 1145: Harry and his brother the Duke of Cambridge are expected to appear at the Chapel's West Steps, probably on foot, walking past the thousands of spectators invited into the grounds of the castle.
This will give Harry an opportunity to acknowledge the 200 representatives from charities he is associated with gathered in the Horseshoe Cloister at the bottom of the steps.
Around 1155: Following protocol, the Queen will be the last member of the Royal Family to arrive.
Around 1159: With a minute to go, Meghan Markle is expected to turn up at the Chapel's West Steps by car, from her overnight accommodation, with some of her bridesmaids and pageboys. She will start her journey, which will take her past some of the crowds in the Long Walk, with her mother Doria Ragland - but when the car stops at the castle her mother will exchange places with her bridesmaids and pageboys, including Princess Charlotte and Prince George. Ms Ragland will enter the chapel by the Galilee Porch.
Noon: The service starts. Everyone will already know most of what to expect as the order of service is being released at midnight on Friday.
Around 1300: The newlyweds will emerge about an hour later at the West Steps of the Chapel. They will be waved off on their carriage procession through Windsor by members of both families. The congregation will file out of the chapel to see the newlyweds leave before heading to St George's Hall for the lunchtime reception hosted by the Queen.
The carriage procession through the streets of Windsor is expected to take about 25 minutes.
1900: The reception is not being televised and neither is the evening reception at Frogmore House, but viewers will get another glimpse of the royal couple when they leave Windsor Castle at 7pm for the evening do, which is hosted by the Prince of Wales.