It celebrates Jesus' arrival in Jerusalem for the Jewish festival of Passover.
Great crowds of people lined the streets waving palm branches to welcome him.
The people were very excited.
They spread branches on the road – and even laid down their clothes.
They shouted 'Hosanna!' which means 'Save us Now!'
The Sunday before Easter is called Palm Sunday because the crowds waved palm branches as they followed Jesus' procession into Jerusalem.
It was the time of the Jewish feast of Passover. Many Jews travelled to Jerusalem to celebrate this feast together.
On Palm Sunday, children are given crosses made from single palm leaves. Traditionally, many churches will have a procession in or around the church while people sing songs of praise and wave palm leaves. This is to help them imagine what Jesus' entry into Jerusalem might have been like.
In some churches small buns called pax cakes (symbolic of peace and goodwill) are given to the congregation as they leave after a Palm Sunday service.
Any left over Palm Crosses are kept and burned to make ashes for next years Ash Wednesday services (see Ash Wednesday )