But unlike regular weddings, these ones involve an elaborately choreographed event that will be watched by an audience of millions.

One of the first decisions a couple makes is deciding where to actually do the thing.

If they are really into history and tradition, there's really only one choice: "From the solemnity of the abbey."

But not this time.

The big change is this wedding between Prince Harry and Meghan Markle.

You don't have all the ambassadors from all the different countries, you don't have heads of state coming to this wedding.

One reason is because the Chapel Windsor can only take 600 people and therefore there simply isn't space.

But it's also clearly the desire of Prince Harry and Meghan Markle to have a more informal wedding.

At around two months before the big day, the Lord Chamberlain's office sends out individually handcrafted invitations.

There's flowers and fittings and the entirety of the city to prepare.

While the bride and groom head to sleep in different homes — spectators who want a decent view of the public processions will be sleeping outside.

And just a few hours later, Some have traveled hundreds or even thousands of miles and they camped out overnight to get a prime position along that procession route.

The general rule of royal weddings is the the less important you are, the earlier you arrive, and the farther back you sit.

If you're there representing a charity, if a member of the armed forces, or a celebrity, you're relegated to the nave of the church, which means you might not even get to see the actual ceremony.

Close friends of the bride and groom and other guests will head in at least an hour and a half before.

Most of the time it is: groom up at the front.

The royal procession comes in order In order of precedence, which means the more junior royals come first and last comes the Queen and her husband Prince Philip.

Lots of fanfare as they come and then the bride turns up.

When the bride arrives, the details of the dress are finally revealed after months of top secrecy.

I am beside myself. This is such a fashion moment, I can't tell you.

And regardless of who the designer is, she'll be wearing white and will carry a sprig of myrtle in her bouquet, which symbolizes love and marriage — both of which are trends started by Queen Victoria.

The bride's tiara is almost always the "something borrowed," likely from one of the family's collections of jewels.

Since 1923, the ring placed on the bride's finger is always made from Welsh gold — Elizabeth and Diana's rings even came from the same nugget.

The ceremony's performed by the Archbishop of Canterbury and only takes about an hour.

Towards the end, the bride, groom, and their two witnesses go into a private room to sign the registrar.

At that point the wedding is sanctified in law, as it was sanctified by religious service a few minutes previously.

Officially married, the bride and groom exit, closely followed by the Procession of the Queen.

If there's any heart that hasn't been run over by her today, it can kindly surrender now.

There's a good chance you'll hear "Pomp and Circumstance" around this time — although Americans associate it with high school graduations, it was originally written for the coronation of King Edward VII.

The bride and groom will likely make their way into the open 1902 State Landau for the official carriage procession around the city — that's when the crowds who have been waiting for hours, or possibly days, will get their first look at the royal couple.

This usually concludes with the iconic appearance on the Buckingham Palace balcony — on which Diana and Charles were the first to kiss.

The kiss is a critical moment in the entire royal wedding ceremony.

You don't just throw it away in the middle of church.

It has to be seen live by hundreds of thousands of peoples.

And just in case anyone had missed it, Prince William suggests one more kiss.

Because Meghan and Harry's wedding is 20 miles outside of London, their first public kiss as a married couple will have to happen someplace else.

Afterwards, the wedding party takes official photos, and ceremony guests gather for the "wedding breakfast," complete with a traditional fruit cake.

Though in the past the bride and groom would change clothes and depart for their honeymoon directly afterwards, current royals have gone for a more modern approach with a real party.

And they won't be the only ones celebrating.

It is generally seen as an excuse to have a good time and somewhat buttoned-up Brits who don't really have a good time in public that much, let their hair down and enjoy themselves in the middle of their street.

At that point it's a pretty normal wedding reception —although normal ones don't generally include (rumoured) performances by Elton John and the Spice Girls.

The royal couple will head off for the honeymoon — which is almost certainly within the British Commonwealth, while the rest of the country nurses a hangover.

As they leave far behind them, an exhilarated, exhausted London, for them, as for any newlyweds, the adventure is just about to begin.