The monarch said she was delighted to be in Perth "for a meeting that promises to bring new vibrancy to the Commonwealth".
Australian Prime Minister Julia Gillard, the host, told the gathering that it was vital for the Commonwealth bloc to move with the times.
"The world has changed, and a wise institution changes too," she said.
"So as the Commonwealth journeys towards its centenary, it is time for renewal. To answer the question posed of our organisation -- how do we best pursue our timeless values in a world of change?
"Let us make CHOGM 2011 memorable for answering this question. Memorable for being the meeting that gave the Commonwealth the direction it needed at a time of global uncertainty and risk.
" Outside the summit venue, thousands of police were on city streets with the centre of