The Queen has opened a two-day summit of leaders of the 53 Commonwealth nations in Malta.
The Commonwealth Heads of Government Meeting (Chogm), held every two years, will focus on climate change, with talks on security issues also expected.
UK Prime Minister David Cameron has pledged to set up a Commonwealth unit to target the “scourge” of extremism.
The group of nations has a vital role to play in tackling terrorism, he said, and pledged £5m to help fund the unit.
Security was high around the Queen as she arrived with the Duke of Edinburgh, the Prince of Wales and Duchess of Cornwall.
Opening the conference, the Queen said she was enormously proud of what the Commonwealth had achieved and “all of it within my lifetime”.