One of the earliest places in the world to celebrate the start of the year 2010 was Sydney in Australia. Around 1.5 million people crowded into the harbour to watch.
The fireworks display was a little smaller in Baghdad in Iraq.
Around 120,000 people crowded into Moscows' Red Square in Russia.
In Berlin in Germany around a million people were expected near the famous Brandenburg Gate to celebrate the new year.
In Paris officials decided against a fireworks display. Instead they produced an amazing light show using lasers for around 70,000 people.
In London people were treated a seven-and-a-half minute fireworks display, centred on the London Eye on the South Bank of the River Thames.
In Edinburgh around 80,000 braved temperatures that were below zero when midnight was struck.
One of the biggest parties was in Rio de Janeiro in Brazil, where around two million people crowded onto beaches to watch the display.
In New York, America people partied in Times Square, where very high levels of security were in place to keep them safe.
Las Vegas was another popular place for Americans to mark the beginning of 2010.