From the Treasury of Daily Prayer:

The Easter season is a fifty-day-long season of joy extending from Easter to Pentecost. During this time, the Church celebrates the end of Christ’s struggles and proclaims His victory over death and the reception of the benefits of His life, death, and resurrection as gracious gifts of love and mercy for all those who believe in Him. This is the Church’s great season of joy! Christ is risen! He is risen indeed. Alleluia!