Thanksgiving is upon the US, with an estimated 46m turkeys due to be eaten over the weekend as the country celebrates.

A national holiday since 1863, families across the nation come together to mark the occasion a month before Christmas.

When is Thanksgiving?

Although it was Abraham Lincoln that first proclaimed a "day of our annual Thanksgiving", it wasn't until Franklin D Roosevelt's presidency that the holiday was officially scheduled for the fourth Thursday in November.

The holiday had been celebrated sproadically up until the 19th century, usually after major events – George Washington proclaimed a Thanksgiving in 1789 to celebrate the new country's freedom from British rule.

When was the first Thanksgiving?

The first Thanksgiving is generally believed to have occurred in 1621 when Puritan pilgrims who first settled in New World to escape persecution in Europe arrived on the Mayflower.

Their first harvest had failed and were, according to legend, saved by the Wampanoag Indians, who believed they may be useful allies in their war against a rival tribe – the Narragansett.

It was unlikely to have been called a Thanksgiving at the time but the name caught on and there were occasional celebrations of the event over the course of the next centuries – usually after settlers had either fended off an Indian attack or cruelly massacred a Native American settlement themselves.

Why do people celebrate Thanksgiving?

To many Americans, Thanksgiving represents an important part of America's founding myth.

The Mayflower pilgrims were one of the first groups to settle up a permenant, surviving colony in modern-day Cape Cod, Massachusetts.

Today's Google Doodle in the US celebrates the holiday

Many previous attempts had ended in failure – most notably the Roanoke Colony which disappeared or was abandoned sometime before 1590.