Security was tight, some events were called off and in Munich two train stations were closed, all over fears of terror threats, but around the world revellers took to the streets to welcome the new year.
Europe ushered in the new year amid heightened security fears as German police evacuated two train stations in Munich, citing a tip about a planned militant attack, and Belgium arrested three people over an alleged plot.
In the United States, federal authorities said an ex-convict seeking to prove he was worthy of joining Isis (Islamic State) planned to carry out a New Year's Eve attack at an upstate New York bar using a machete and knives provided by an FBI informant and was arrested in an FBI sting.
In New York, about 1 million people crammed into the Crossroads of the World, brushing off security jitters to watch the glittering crystal ball drop in Times Square, marking the start of 2016.
A record number of police officers patrolled the event. Heavily armed officers stood on nearly every corner as others with rifles and binoculars surveyed the crowd from rooftops above.
But as the Waterford crystal ball descended, revellers counted down to 2016 before sharing hugs and their first kisses of the year under a blanket of confetti.
Security forces in many capitals were on raised alert after a year of militant attacks, the biggest of which killed 130 people in Paris in November and was claimed by Isis.
Soldiers were on the streets of Paris and police forces in London, Madrid, Berlin and Istanbul increased their presence as Europeans turned out to celebrate.
Celebrations in Germany took on a sombre note when police warned of a possible terror attack and evacuated two train stations in Munich.
A police spokeswoman said a search for possible suspects had been launched and a tweet from German police said "we take the threat very seriously".
Bavaria's Interior Minister, Joachim Herrmann, said authorities had received information that Isis was behind the threat.
Munich police president Hubertus Andrae said German authorities had been tipped off by a foreign intelligence service that Isis was planning attacks with five to seven suicide bombers, the German news agency DPA reported. Andrae said so far there hadn't been any arrests.
Police spokesman Werner Kraus told the Associated Press that "after evaluating the situation, we started evacuating the train stations and also asked partygoers to stay away from big crowds outside".
The warning came only hours before the city rang in the new year.
Despite police warnings to stay away from big crowds, thousands of people were on the streets of Munich at midnight to welcome the new year with fireworks.
In the US, prosecutors said Emanuel Lutchman, 25, of Rochester, was charged with attempting to provide material support to terrorists. Officials said he was caught in an FBI sting involving three paid informants.
Lutchman is a self-professed convert to Islam who claimed to receive direction from an overseas Isis member and planned to carry out an attack at a bar-restaurant in Rochester on New Year's Eve, authorities wrote in court papers. The name of the business wasn't released.
According to the FBI, Lutchman and an informant bought knives, a machete, ski masks and plastic cable ties for the attack. Lutchman had no money, so the informant paid for the items, according to the complaint filed in federal court in Rochester.
Lutchman was arrested the day before New Year's Eve.
In Belgium, police were holding three people for questioning as part of an investigation into an alleged plot to carry out an attack in Brussels on New Year's Eve. Authorities on Wednesday called off the usual New Year's Eve fireworks display in the capital, citing fears of a possible militant attack.
Police had initially detained six people after searches at six locations in the Belgian capital and one just outside the city. They also seized computers, mobile phones and equipment for airsoft, a sport using guns that shoot non-lethal plastic pellets.
Three of the six were released. Prosecutors said they were holding the other three for a further 24 hours.
French President Francois Hollande, meanwhile, said his country was "not finished with terrorism" and used a New Year's message to defend controversial plans to strip citizenship from those convicted of terrorism offences.
"The threat is still there," he said in a televised address. "It remains in fact at its highest level, and we are regularly disrupting planned attacks."
In Istanbul, police said they had ramped up the number of officers on the streets by about 10,000.
Turkish police on Wednesday detained two suspected Isis members they believe to have been plotting New Year's Eve suicide attacks in the capital Ankara, where less than three months ago a double suicide bombing killed more than 100 people.
While many people turned out for public New Year celebrations, the year of militant attacks produced more of a mood of worry and uncertainty for others.
"Normally, I go out to the bars on the Asian side of Istanbul," said 26-year-old IT expert Seyda Yilmaz. "But this year, because of the danger of Isis, I will spend New Year's Eve in my home."