Advent Sunday, also called the First Sunday of Advent or First Advent Sunday, among the Western Christian Churches, is the first day of the liturgical year and the start of the season of Advent.

Advent is a season observed in most Christian denominations as a time of expectant waiting and preparation for both the celebration of the Nativity of Christ at Christmas and the return of Christ at the Second Coming. Advent is the beginning of the liturgical year in Western Christianity. The name was adopted from Latin adventus "coming; arrival", translating Greek parousia from the New Testament, originally referring to the Second Coming.