The APEC summit is happening this week in San Francisco. What is APEC, anyway?

WASHINGTON (AP) — The United States is hosting the annual APEC summit of world leaders this week for the first time since 2011. Leaders from the 21-member Asia-Pacific Economic Cooperation group will gather in San Francisco to talk about how to better spur trade and economic growth across the Pacific region.

But the main summit event will actually be on the sidelines: A face-to-face meeting between President Joe Biden and Chinese President Xi Jinping. This year's conference is happening against the backdrop of the frosty relationship between China and the U.S. and global turmoil from the Israel-Hamas war and Russia's invasion of Ukraine.

A look at what APEC is and how it works:

WHAT IS APEC?

APEC stands for Asia-Pacific Economic Cooperation. It's a forum to promote trade, investment and economic development among nations around the Pacific Ocean.

The group started with 12 members in 1989, but has since grown to 21 including China, Russia, Japan, the U.S. and Australia. Those member nations pack a lot of punch, accounting for nearly 40% of the global population and almost half the world’s trade.

The annual leaders' conference brings together heads of nations and other top economic and diplomatic leaders. (Don't expect much of a presence from Russia this year; it's a pariah as Russian President Vladimir Putin presses his country's invasion of Ukraine and will have lower-level representation.)

White House aides say the goal for this year's summit is to try to make APEC economies more resilient, particularly in the face of growing climate issues and following a global pandemic that killed millions of people and strained supply chains.

THE MAIN EVENT

The main event of this summit is unfolding on the sidelines: a meeting between Biden and Xi. The two leaders haven't spoken in person since they met last November during the Group of 20 summit in Bali, Indonesia. A lot has happened since then to ratchet up tensions between the superpowers.

The Biden administration shot down a Chinese spy balloon that traversed the continental U.S. earlier this year. The Chinese government hacked the emails of Commerce Secretary Gina Raimondo. The U.S. government restricted the export of advanced computer chips to China, and has pushed to provide development aid to other nations to counter China's influence.

The differences also have been exacerbated by Russia’s war in Ukraine and China’s increasing assertiveness in the Taiwan Strait. But representatives from the U.S. and China have been meeting with increasing frequency lately, working to thaw relations. Still, the Biden-Xi meeting isn't expected to substantially alter the trajectory of U.S.-China relations.