Like so many other good traditions, Halloween started in Ireland.
The Government's put together a video explaining the origins of the holiday.
It started with the ancient Celts over 1,000 years ago, who called it Samhain, and was seen as a celebration of the harvest and preparation for winter.
The Celts believed that on Samhain, the souls of the dead would visit their homes - and that those who had died in the past year would travel to the next world.
People would also wear masks to disguise themselves from the visiting spirits.
Large bonfires were also lit to try and ward off the evil spirits that visited on the night.
After the bonfires, people would hollow out turnips and carry an ember of the bonfire home.
The Irish also forecast future happenings at Halloween: by baking barm brack and roasting nuts to predict marriages.
But the tradition of carving turnips was changed when emigrants went to America in the 19th century.
Instead they carved out pumpkins, because turnips were so hard to find.