"Rorate caeli" or "Rorate coeli" are the opening words of Isaiah 45:8 in the Vulgate. The text appears at several points in the Christian liturgy of the Western Church during 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.