Samhain, better known as Halloween, is a sacred witch holiday on which the 'veil' between the living and the other side is at its thinnest. It is usually celebrated on October 31st. Although Samhain is predominantly celebrated by witches in the Night World series, humans and other Night People such as vampires are known to celebrate it as well.
Samhain has presumably been celebrated by the witches for many centuries - it is unclear how long exactly. Thea and Blaise Harman mention secretly watching the Inner Circle perform a summoning ritual one Samhain, a year before the events of Spellbinder. Humans usually call Samhain Halloween, derived from 'All Hallows Eve', as October 31st is the day before All Saints Day (November 1st). Although this is considered a Christian holiday, Halloween's roots are found in the beliefs and traditions of the Ancient Celts (whose traditions are still practiced by witches).
Few humans regard Halloween as being a religious holiday anymore; Halloween as it is celebrated by most humans (with costume parties, 'trick-or-treating' and candy) became popularized in the early to mid 20th century. However, the witch traditions in regards to Samhain have presumably remained the same for generations. Witches regard Samhain as a time to gather together with friends and family, reflect on who are are or who they want to become and to remember and honour those who have passed on.
After dropping her granddaughters off at their new school, Grandma Harman warn Thea and Blaise Harman to behave until the end of the month, which happens to be Samhain when the Inner Circle will perform their annual summonings of the ancestors in Las Vegas. (more to be added)
Humans celebrate Samhain by putting on costumes, however, witches attire themselves by reflecting their personal or favorite deity. Vampires are known to host parties or stay inside in front bonfires, while human children have a tradition known as "trick-or-treating" by going around to houses asking for treats.
Witches gather in groups known as "Samhain Circles", where they would meet up and celebrate Halloween by performing magic rituals. A Circle Twilight group was seen preparing a circle presumably for their Samhain rituals, however, it was interrupted and never seen completed. The Inner Circle is known to commune with their ancestors on Samhain, and sending-back spells are known to be best performed on Samhain night as well, clearly shown by Thea when she returns Suzanne Blanchet to the beyond the veil.
- Thea Harman: Hellewise Hearth-Woman
- Blaise Harman: Maya Hearth-Woman
- Eric Ross: 17th century soldier at Ron-chain
- Dani Abforth: Queen Isis (Egyptian mother goddess)
- Lawai'a Ikua: Pele (Hawaiian fire goddess)
- Nathaniel Long: Herne (Celtic god of hunting)
- Kishi Hirata: Amaterasu (Japanese sun goddess)
- Alaric Breedlove: Tammuz (Mesopotamian shepherd god)
- Claire Blessingway: Changing Woman (Navajo goddess)
- Chang Xi: Kuan Yin (Chinese goddess of compassion)