Revelers across the Pacific Islands, Asia, Africa, and Europe have welcomed 2011 with celebrations and fireworks displays, and crowds are already gathering across the Americas to mark the start of the new year there.
The tiny Pacific island nation of Kiribati was the first to ring in 2011.
London hosted one of Europe's biggest celebrations, on the banks of London's River Thames. Around a quarter of a million people gathered to watch fireworks as the famous Big Ben at Parliament chimed in the new year.
But an even larger celebration is getting underway in New York City, where organizers say a million people will crowd into Times Square for the annual drop of a huge, sparkling ball from high above. The Waterford Crystal ball weighs 5,400 kilograms.
Earlier on the other side of the world, New Zealanders welcomed 2011 with a spectacular firework show in Auckland and celebrations elsewhere, while in Sydney, Australia, at least 1.5 million people gathered for the annual fireworks show on the Harbour Bridge.
China's president Hu Jintao addressed his country on New Year's Eve, pledging peaceful international relations while pushing for a transformation of the country's export-driven economy.
Video snippets from around the World
And at midnight in Dubai, fireworks exploded from all sides of the world's tallest building.
In Vatican City, Pope Benedict held a prayer service at St. Peter's Basilica. He is scheduled to hold a Mass on New Year's Day.
New Year Celebrations around the World Slide Show