Fireworks were set off and 3,000 pounds of confetti were scattered when the gigantic New Year's Eve crystal ball drops at midnight. Many people wore conical party hats and 2010 glasses that blinked colorfully, and some were jumping up and down to keep warm - the National Weather Service said the temperature would be around freezing and predicted snow.
Cellphones were brought out to document the last few hours of a decade many wanted to leave behind. The crowds brought out heightened security. Hundreds of officers were scattered around Times Square. Snipers were at various locations.
From fireworks over Sydney's famous bridge to balloons sent aloft in Tokyo, revelers across the globe at least temporarily shelved worries about the future to bid farewell to "The Noughties" - a bitter-tinged nickname for the first decade of the 21st century playing on a term for "zero" and evoking the word naughty.
Paris jazzed up the Eiffel Tower with a multicolored, disco-style light display as the world basked in New Year's festivities with hopes that 2010 and beyond will bring more peace and prosperity.
Las Vegas welcomed some 315,000 revelers with fireworks from casino rooftops, a traffic-free Las Vegas Strip and toasts at nightclubs from celebrities including actress Eva Longoria and rapper 50 Cent.
Even as some major stock market indexes rose in 2009, the financial downturn hit hard, sending many industrial economies into recession, tossing millions out of work and out of their homes as foreclosures rose dramatically in some countries.
"The year that is ending has been difficult for everybody. No continent, no country, no sector has been spared," French President Nicolas Sarkozy said on national TV in a New Year's Eve address. "Even if the tests are unfinished, 2010 will be a year of renewal," he added.
German Chancellor Angela Merkel warned her people that the start of the new decade won't herald immediate relief from the global economic ills. South Africa's president, Jacob Zuma, was more ebullient, saying the World Cup is set to make 2010 the country's most important year since the end of apartheid in 1994.
At midnight in Rio de Janeiro, about 2 million people gathered along the 2.5-mile (4 kilometre) Copacabana beach to watch a huge fireworks display and listen to dozens of music acts and DJs.
The multitudes came mostly dressed in traditional white clothing, a nod to the Afro-Brazilian religion of Candomble but a custom followed by nearly everyone as it is thought to bring peace and good luck for the coming year.
Officials said about 12,000 police were on duty during the New Year's Eve party in and around Copacabana to provide security.
Dressed in white and holding a glass of champagne in his hand, visitor Chad Bissonnette, 27, a nongovernmental group's director from Washington, D.C., said, "This year was the toughest I've experienced - for the first time as an American I saw many friends lose jobs and businesses in my neighbourhood close regularly."
In New York's Times Square, organizers mixed about 10,000 handwritten wishes into the confetti that was dropped over the crowds. They include appeals for the safe return of troops fighting overseas and continued employment.
Gail Guay, 50, of New Hampshire had this advice: "Don't look back."
Her friend Doreen O'Brien, 48, of New Hampshire, said that the crowd in Times Square seemed to be feeling positive on the cusp of a new decade. "People are in a great mood; it's very friendly. It's like New York has slowed down."
The hundreds of thousands of revelers in New York City brought out heightened police security, displayed a day earlier when police evacuated several blocks around Times Square to investigate a parked van without license plates. Only clothing and clothes racks were found inside.
Police and other officials planned sweeps to detect traces of radiation or biological agents in the area, while a command centre was to be staffed by FBI, New York and regional police.
Australian Prime Minister Kevin Rudd hailed events in 2009 like the inauguration of the United States' first black president, and international attempts to grapple with climate change and the global financial crisis.
"The great message from 2009 is that because we've been all in this together, we've all worked together," Rudd said in a New Year's message.
Australia got the some of the festivities rolling, as Sydney draped its skies with explosive bursts of crimson, purple and blue to the delight of more than 1 million New Year revelers near the harbour bridge.
Concerns that global warming might raise sea levels and cause other environmental problems were on the minds of some as the year ended.
Venice revelers rang in the New Year with wet feet as high tide on its archipelago peaked just before midnight to flood low-lying parts of the city - including the St. Mark's Square.
The last year also offered its reminders of the decade's fight against terrorism, wars in Iraq and Afghanistan, and more recently, rising militant violence in Pakistan.
Prime Minister Gordon Brown of Britain, in a statement Wednesday, suggested that terrorism book-ended the decade, with the Sept. 11, 2001, attacks in the United States, and foiled plot by a Nigerian man to set off explosives on a U.S.-bound airliner on Christmas Eve.
"In late December we were reminded at this decade's end, just as we were at its beginning, that there is a terrorist threat which puts our safety and security at risk and which requires us to take on al-Qaeda and the Taliban at the epicentre of global terrorism," he said.
The American Embassy in Indonesia warned of a possible terrorist attack on the resort island of Bali on New Year's Eve, citing information from the island's governor - though local security officials said they were unaware of a threat.
In a more upbeat theme, the Eiffel Tower was decked out for its 120th anniversary year with hundreds of multicolored lights along its latticework. It was seemingly retro in style, but decidedly 21st century as it showered the Iron Lady in a light show billed as more energy-saving than its usual sparkling lights.
Police blocked off the Champs-Elysees to vehicle traffic as partygoers popped champagne, exchanged la bise - the traditional French cheek to cheek peck - or more amorous kisses to celebrate the New Year.
Spain rang in the start of its six-month presidency of the European Union with a sound and light show illuminating Sol square in Madrid and images from the 27 member states projected onto the central post office building.
Partiers braved the cold - and a shower from sparkling cava wine bottles - in traditional style by eating 12 grapes, one with each tolling of the city hall bell.
Despite frigid temperatures, thousands gathered along the River Thames for fireworks were fired from the London Eye attraction just as Big Ben struck midnight - an hour after continental western Europe.
Europe and the Americas may have partied harder than Asia. Islamic countries such as Pakistan and Afghanistan use a different calendar; China will mark the new year in February.
Still, in Shanghai, some people paid 518 yuan ($75) to ring the bell at the Longhua Temple at midnight and wish for new-year luck. In Chinese, saying "518" sounds like the phrase "I want prosperity."
In the Philippines, hundreds of people were injured by firecrackers and celebratory gunfire during the celebrations. Many Filipinos, largely influenced by Chinese tradition, believe that noisy New Year's celebrations drive away evil and misfortune - but some carry that belief to extremes.
At Zojoji, one of Tokyo's oldest and biggest Buddhist temples, thousands of worshippers released clear, helium-filled balloons to mark the new year. Nearby Tokyo Tower twinkled with white lights, while a large "2010" sign glowed from the centre.
Tokyo's Shibuya area, known as a magnet of youth culture, exploded with emotion at the stroke of midnight. Strangers embraced spontaneously as revelers jumped and sang.
In Istanbul, Turkish authorities deployed some 2,000 police around Taksim Square to prevent pickpockets and the molestation of women that have marred New Year celebrations in the past. Some officers were under cover, disguised as street vendors or "even in Santa Claus dress," Istanbul Gov. Muammer Guler said.
In Stonehaven, on Scotland's east coast, the fireballs festival - a tradition for a century and a half - saw in the New Year. The pagan festival is observed by marchers swinging large, flaming balls around their heads. The flames are believed to either ensure sunshine or banish harmful influences.
In contrast to many galas worldwide, the Stonehaven Fireballs Association warned those attending not to wear their best clothes - because "there will be sparks flying along with smoke and even whisky."