The Queen will officially open the Commonwealth Heads of Government Meeting (Chogm) in Malta.
She will open the summit in Valletta with a speech to the delegates, presidents and prime ministers from many of the member states.
David Cameron is expected to attend the event as is Foreign Secretary Philip Hammond.
The event will take place on the second day of the Queen's tour of the island, accompanied by the Duke of Edinburgh, the Prince of Wales and the Duchess of Cornwall.
The Queen will make a short speech at the opening ceremony, following by words from Malta prime minister Dr Joseph Muscat and other dignitaries.
There will also be an opening performance which will feature more than 360 artists and performers, including the Maltese Philharmonic Orchestra and tenor Joseph Calleja.
After the event the Queen and Charles will hold a reception for new Commonwealth heads of government.
This evening the royals will attend a Chogm banquet at the Corinthia Palace Hotel in Valletta.