In ancient times, palm branches symbolized goodness and victory. They were often depicted on coins and important buildings. Solomon had palm branches carved into the walls and doors of the temple (1 Kings 6:29). Again at the end of the Bible, people from every nation raise palm branches to honor Jesus (Revelation 7:9).
Palm Sunday commemorates the entrance of Jesus into Jerusalem (Matthew 21:1-9), when palm branches were placed in his path, before his arrest on Holy Thursday and his crucifixion on Good Friday. It thus marks the beginning of Holy Week, the final week of Lent.
In the Catholic Church, palm fronds are blessed with holy water outside the church building. A solemn procession also takes place. It includes the normal liturgical procession of clergy and acolytes, the parish choir, and the entire congregation.
In the Catholic Church, this feast now coincides with that of Passion Sunday, which is the focus of the Mass which follows the service of the blessing of palms.