Hail Mary, full of grace, the Lord is with thee. Blessed art thou among women, and blessed is the fruit of thy womb, Jesus. Holy Mary, Mother of God, pray for us sinners, now and at the hour of our death. Amen.
In Latin
Ave María, grátia plena, Dóminus tecum. Benedícta tu in muliéribus, et benedíctus fructus ventris tui, Iesus. Sancta María, Mater Dei, ora pro nobis peccatóribus, nunc et in hora mortis nostræ. Amen.
History
The first part comes from the Angel Gabriel's greeting to Mary (Luke 1:28) and Elizabeth's greeting (Luke 1:42). The second part was added by the Church over time.
When to Pray
Catholics often pray the Hail Mary throughout the day, especially as part of the Rosary and the Angelus.