Leaders of the G20 nations are gathering for a meeting at which they are expected to sign an agreement to fight tax avoidance by multinationals.
The group formally backed plans to tackle international tax avoidance and evasion at its meeting in July.
The gathering, in the Russian city of St Petersburg, is officially about global economic matters.
However, the most meaty topic of conversation is likely to be Syria and how to handle the crisis there.
The meeting, between representatives of the countries that account for two-thirds of the world's population, will also ponder the effects of an end to the US financial stimulus programme.