In parts of Asia, the threat of terrorism loomed large, and a bombing at a market in Indonesia killed eight people and wounded 45.
But celebrations worldwide were generally jubilant, in contrast with last year when the devastation of the Indian Ocean tsunami led many countries and individuals to cancel festivities.
Hundreds of American soldiers in Iraq got a special show from "American Idol" singer Diana DeGarmo and other entertainers at Camp Victory in Baghdad.
More than 2 million Brazilians were expected at jam Rio de Janeiro's famed Copacabana Beach for the largest fireworks extravaganza in the city's history. Officials planned to set off nearly 25 tons of fireworks.
London saw many subway workers walk out just hours before a huge open-air celebration in Trafalgar Square and other parties around the capital.
"I am not worried about the strike; I'm just going to take a cab or use the buses," said Matthew Lapalus, a 22-year-old Frenchman who came to London to celebrate New Year's Evens of fireworks..
London Underground said it hoped workers not affiliated with the striking RMT union would keep much of the network running. By early evening, only about 30 of the Tube's 275 stations were closed as managers sought to keep some trains going.
In France, 25,000 police were on alert, fearing a repeat of arson attacks and rioting that swept the country for three weeks starting in late October.
"The orders I have given are very strict," said French Interior Minister Nicolas Sarkozy. "When there are delinquent acts there will be arrests. Those guilty must be accountable for their acts."
Burning cars is common in troubled French neighborhoods — dozens of vehicles are set afire on an average night and in recent years the figure has risen to about 300 on New Year's Eve. But police were especially cautious this year and a state of emergency imposed during the rioting was still in effect.
The mood was more festive elsewhere.
Four months after Hurricane Katrina, New Orleans residents prepared to ring in 2006 with fireworks and concerts.
"New Orleans is back open, so come on down and start visiting. That's the word to get out," said Brian Kern, an organizer of the festivities, which were paid for by businesses because the city's tax income was wiped out by the storm.
In Australia, revelers jostled for vantage points around Sydney's harbor to watch a spectacular fireworks show at midnight.
"You can't beat the setting," said Andrew Coomer, a 21-year-old English tourist who camped with his family outside the Sydney Opera House for 12 hours to catch the fireworks.
More than 1,700 police officers were on duty for the night and police helicopters and boats buzzed across the harbor — a huge presence aimed at preventing a repeat of racial violence that broke out in the city's southern beachside suburbs earlier this month.
Suspected Islamic militants tried to make a statement in Indonesia today, setting off a bomb packed will nails in a busy market, reports CBS News correspondent Sharyn Alfonsi, killing eight people and wounding 45. The market in Palu on Indonesia's Sulawesi Island, which has been plagued by religious violence and terrorism by radical Muslims, is frequented by Christians.
In Bangladesh, 5,000 security officers searched cars and patrolled the streets of the capital to thwart possible violence in the wake of a series of bombings blamed on Islamic extremists that have killed at least 26 people.
For the millions left homeless by this year's South Asian quake, the new year was expected to begin with heavy snow and rain. Relief agencies warned that the harsh Himalayan winter could hamper aid deliveries and create conditions ripe for illnesses.
Pakistan's army and aid workers have been using helicopters, trucks and mules to get tents, clothes, food and other provisions to survivors since the Oct. 8 quake killed an estimated 87,000 people and destroyed the homes of 3.5 million others.
In Japan, police expected more than 14,000 people to climb the 12,387-foot, snowcapped Mount Fuji and other mountains before dawn to see the first sunrise of the new year.
But a new holiday pastime also has emerged among Japanese — watching professional wrestling on TV — and many rang people in the new year glued to their sets.
In the Philippines, two people were reported killed by bullets fired during celebratory gunfire and two others died after eating a popular sparkler that looks like candy. Firing guns in the air is a traditional way for Filipinos to welcome the new year.