The Queen is to address the Scottish Parliament as part of its 20th anniversary celebrations.
The Prince of Wales will join his mother as she makes a speech to MSPs in the debating chamber.
The ceremony takes place almost 20 years to the day since the Parliament officially assumed its legal powers on July 1, 1999 following devolution.
Some of the young people born on that date will join MSPs to hear the Queen’s speech.
The Crown of Scotland will be brought in a procession from Edinburgh Castle to the Parliament and enter the chamber, along with the Scottish Parliament Mace, to a fanfare sounded by the Royal Conservatoire of Scotland, ahead of the Queen’s arrival.
The royal visitors will be welcomed by Presiding Officer Ken Macintosh before making her address.
First Minister Nicola Sturgeon will make a speech in response, as will Scottish Conservative leader Ruth Davidson and Scottish Labour’s Richard Leonard.
They will be followed by Scottish Green co-convener Patrick Harvie and Liberal Democrat MSP Tavish Scott.
The speeches will be interspersed with cultural performances, including Scots Makar Jackie Kay reading her poem The Long View, written specially for the event and celebrating the changes in the 20 years since the Scottish Parliament was reconvened.
The chamber choir of the National Youth Choir of Scotland, Scottish folk musician Phil Cunningham and members of Celtic band Capercaillie will also perform.
Stuart MacMillan MSP will play Robert Burns’s A Man’s A Man For A’ That on the bagpipes as the Queen leaves the chamber.
After the ceremony, the Queen and Charles, who is known as the Duke of Rothesay in Scotland, will attend a reception in the Parliament’s main hall and sign the visitors book.
When the Queen’s visit was first announced, Mr Macintosh said: “Since the Scottish Parliament was established nearly two decades ago, Her Majesty the Queen has given us her unwavering support.
“She addressed the newly elected MSPs in July 1999 as we assumed our legislative powers and she has visited Holyrood many times since. Each time with messages of friendship and support.
“It will be a pleasure to welcome Her Majesty and HRH the Duke of Rothesay to the Parliament once again as we celebrate our 20th year.”
The visit will be the ninth time the Queen has addressed the Scottish Parliament.
Her last speech to MSPs took place on July 2 2016 as part of celebrations marking the opening of the fifth session of the Parliament.
Charles last visited the Parliament in 2006 to attend a reception of the Prince’s Trust.
The ceremony on Saturday is part of a year-long programme of events to mark two decades of devolution.