The Commonwealth of Nations summit brings together around a quarter of the world's countries and a third of its population. Extremism and migration as well as the environment are the main issue of the 24th biennial summit.
In the inaugural speech on the Mediterranean island, Queen Elizabeth gave her wishes to the participants. "At this meeting, the Commonwealth will be charged with demonstrating leadership, often in practical ways, on an agenda of global issues."
"I feel enormously proud of what the Commonwealth has achieved, and all of it within my lifetime," the Queen who is head of the Commonwealth since 1952, said.
She also spoke of the Commonwealth's potential to tackle climate change and stressed the importance of getting young people involved in the fight to slow global warming.
The summit comes ahead of a UN climate conference in Paris starting Monday where world leaders will try to open the door to a landmark accord for limiting greenhouse gases.
Countries most at risk -- including low-lying small island states and poor nations in Africa, many of them Commonwealth members -- have called for capping warming to 1.5 C, saying anything less would result in catastrophic impacts.