- Royal matters -
Britain's Queen Elizabeth II had to consent to the wedding, as under British law the monarch must approve the marriage of the six people next in line to the throne in order for them to retain their place.
Harry is currently fifth in line after his father Prince Charles, elder brother Prince William and his sibling's two children, but will be bumped down to sixth place after William's third child is born as expected later this month.
Markle, meanwhile, has been baptised by the Archbishop of Canterbury into the Church of England.
The decision was taken out of respect for Queen Elizabeth's role as the church's supreme governor.
- The guest list -
Some 600 people have been invited to attend the wedding service and the lunchtime reception at St George's Hall within Windsor Castle.
It is still not known who will be Harry's best man and Markle's maid of honour.
Around 200 guests will go on to an evening reception at Frogmore House, a royal residence south of the castle.
A further 2,640 people will be welcomed into the grounds of Windsor Castle, including charity representatives and military veterans, to watch the arrival of the bride and groom and their carriage procession following the ceremony.
US President Donald Trump and British Prime Minister Theresa May have not been invited. Kensington Palace -- the official residence of Harry and Markle -- said "an official list of political leaders" has been deemed unnecessary for the nuptials.