Fireworks and spectacular light displays helped revellers welcome in 2016 across the globe, although several major cities were on high alert as the New Year began.
The atmosphere at the celebrations ranged from carefree to cautious, with uncertainty overshadowing many European cities and terrorist threats cancelling events in Paris and Brussels.
A glittering ball descended on Times Square in New York, keeping with the city's famous New Year tradition.
Confetti flew across the square, where an estimated 1 million people had gathered.
There was trouble further north in New York state, however, where authorities in Rochester cancelled an official fireworks show after a man was accused of an alleged Islamic State-inspired plot to attack a restaurant and bar.
Rio de Janeiro - which has much to look forward to as the host of the 2016 Olympics - celebrated with a huge display of pyrotechnics launched from barges off the Copacabana beach.
There were more muted celebrations in parts of Europe.
Brussels Mayor Yvan Mayeur stopped the Belgian capital's fireworks after learning of an alleged plot targeting major sites in the city during year-end celebrations.
Belgium has been on high alert since the November 13 terrorist attacks in Paris, as many of the perpetrators had links to Belgium.
Paris also cancelled its official New Year's fireworks in favour of more subdued celebrations, with private rockets and fireworks generally banned and the areas around the Eiffel Tower and the Champs Elysees boulevard barricaded.
France instituted a state of emergency after last month's attacks, which left 130 people dead.
One of Paris' most historic sites, the Arc de Triomphe, was however illuminated to welcome in 2016.
Events in the German capital Berlin carried on as planned, but were overshadowed by news of a suspected terrorism threat in Munich shortly before midnight (2300 GMT).
Munich's main railway station and one other station were evacuated before the New Year began, but reopened a few hours later. The threat concerned a planned suicide attack, police said.
Nonetheless, Berlin authorities tightened controls across the 2-kilometre long party venue at the Brandenburg Gate, with visitors subject to a ban on large rucksacks and bags.
Additional security officers were patrolling the streets of London, Rome and New York, while added checks were put in place at open-air parties in Madrid and Moscow.
Some 3,000 officers were deployed in London as thousands massed to see the fireworks along the capital's River Thames.
On the other side of the globe, 1 million people rang in the New Year by watching Australia's famous fireworks display in front of Sydney Opera House.
Midnight struck, launching the biggest-ever New Year extravaganza for the city, with an extra 2,400 fireworks in a 20-minute spectacle.
Across the Tasman Sea in New Zealand's largest city Auckland all eyes were on the Sky Tower’s four-hour light show followed by a huge firework display at midnight.
In China, one of the biggest annual public gatherings - on Shanghai's Bund promenade - was cancelled as a precaution, after 36 people died in a crush at last year's event. Tens of thousands of people normally attend.