Oh yeah — it's a Gaelic festival marking the end of the harvest season and the beginning of winter or the "darker half" of the year. It was mentioned in some of the earliest Irish literature and many important events in Irish mythology happen or begin on Samhain. It was popularized in the late 19th century, but has been linked to All Saints' Day since the 9th century.
Both of these holidays strongly influenced the secular customs of Halloween and it's believed that the veil between our world and the spirit world is especially thin around this time of year, allowing the beings and souls from the Otherworld to come into our world.