What is the Origin of Halloween?

There are many versions to the origin of Halloween but the most common is known to have started with the Druids. They were a Celtic culture that feasted annually on October 31 to honor the dead. They had festivals to mark the end of summer or what they called the Celtic Year and the beginning of a new one. Souls of the dead were believed to roam the streets at night. Because they believed that not all the souls were friendly, they left gifts and treats hoping to appease the evil souls so that they had a good crop the next year. This is how it came to be that we have trick or treating.