It's interesting to learn that the traditional New Year's Day celebration is in celebration of a Pagan Holiday. It's also the only public holiday that is celebrated most in most nations around the world.
In the U.S. we use the Julian Calendar, which was created during the time of Julius Caesar. It's also referred to as the Caesar Calendar. The New Year, January 1, was a celebration of the God Janus, who had two faces: one facing back and one facing forward. This was a god who could look back on last year, and see the year to come.
A new calendar used in most nations around the world is the Gregorian calendar. January one on the Caesar Calendar (adapted in 1752) corresponds to January 14 on the Gregorian scale, and therefore New Year's is celebrated on January 14 in most nations. Still, the celebration is basically on the same day each year.
Some Eastern Orthodox churches use another calendar, yet coincidentally they celebrate the New Year on the same day as us. So it's truly a national celebration.
January, thus, is named after the Pagan go Janus. He was the god of "gates, doors, and new beginnings," according to Wikipedia. The date this celebration is believed to have started is 153 BC, although there is no consensus as to the exact date.
Still, as you can see here, the celebrations vary from nation to nation. And some countries, such as China, celebrate the day on a different day as you and I. In fact, it is known as the oldest holidays, being first celebrated in ancient Babylon some 4,000 years ago.
According to Wilstar.com the New Year did not always start on January 1.
In 2,000 BC the Babylonian New Year was changed to correspond with the first New Moon after the Vernal Equinox (first day of Spring). Wilstar notes that spring (in March) was a better time to celebrate the new year, as spring is a time of everything fresh and new, and January has no such significance.
The Romans celebrated the New Year in late March, although tampering with various Emperors often made the date different until Julius Caesar was in charge of Ancient Rome. The calendar was changed to make the date in synchronization with the sun.
At this time, according to Wilstar, the Roman Senate (in 153 BC) declared January 1 to be the beginning of the New Year. Yet the previous year often dragged on for 445 days so January 1 would be in synchronization with the sun. So you can see the confusion this created.
However, the Julian Calendar ultimately created a set date for January 1 following a 365 day calendar year, or 366 on a leap year.
Since the New Years celebration was originally known as a Pagan holiday, the Catholic Church forbade its celebration. Although later the Christian church placed its own holiday observances on the same day as Pagan celebrations so people would forget about the old reasons for the holiday and remember the Christian reasons for the celebrations.
For example, like New Years, December 25 was originally a Pagan celebration. So the Catholic Church made it so the celebration of the Birth of Jesus was also on that date. This was possible because no one knew exactly when the Birth of Jesus actually was.
During the Middle Ages the Church was opposed to the New Year's Celebration, and it has only been celebrated by Western Societies for the past 400 years.