Large numbers of police have been deployed
Meeting amid tight security, the G20, which brings together 19 nations and the European Union, will examine how the world economy can be made to work to alleviate poverty, and how to cut off funding for extremist groups.
The International Monetary Fund and World Bank are also holding talks in Ottawa, after the attacks in the US led them to postpone a meeting planned for late September.
On the eve of the Ottawa meeting, several hundred anti-globalisation protesters took to the streets and large numbers of police have been deployed ahead of more protests expected later on Saturday.
One issue for the ministers is how to make borders more secure without creating a new barrier to international trade. Another is how to shut down the financing of networks behind terror attacks.
The rich countries have already made a start, agreeing to freeze the assets of people and organisations suspected of being involved. But they are anxious to encourage similar action around the world.
There will also be much discussion of the deterioration of global economic prospects since 11 September.
Argentine confidence
On the edge of the meeting one of the countries most heavily in debt, Argentina, has expressed optimism that it can find a way out of its economic difficulties.
Argentine Economy Minister Domingo Cavallo emerged from a meeting with top US officials in Ottawa, expressing confidence that he will receive support for his plan to reduce his struggling country's debt payments.
"It was an excellent meeting," he told reporters.
Mr Cavallo met US Treasury Secretary Paul O'Neill, Federal Reserve Chairman Alan Greenspan and Undersecretary of International Affairs John Taylor.
Argentina is looking for a way to restructure the $132bn (£92.5bn) in debt it has accumulated, which - at current interest rates - would result in $4bn in interest payments next year.
The country is enduring the 40th month of recession, which shows few signs of abating.