Wassailing is a long withstanding folklore tradition that has been around since the early Middle Ages. The origins of this tradition are murky, but there are several oral folklore stories that mention celebrations akin to wassailing. The first mentions give no mention to the tradition, but instead the name comes from a greeting within those tales that translates to "be in good health" or "be fortunate (Doares). From these Norse greetings and Old English greetings, you get a saying that sounds similar to "wassail" and from there a traditoin was born.
The wassailing tradition has been around for centuries and it is a classic folklore tradition that encompasses verbal and physical folklore (Sims). It involves a song that is sung to grant the singer entrance into a home, where they will receive food and drink. This combination of verbal and physical folklore is seen throughout many countries, and wassailing is a perfect representation within the United Kingdom.
How wassailing has evolved through the ages also shows how folklore is not static. Many traditions within the United Kingdom not only come from older greetings, but they also come from the ancient civilizations that inhabited the country. They have taken from these ancient cultures to bring a uniqueness to this Christmastime tradition, and to influence current generations to revive these old customs.