Pentecost is one of the prominent feasts in the Christian liturgical year commemorating the descent of the Holy Spirit upon the disciples of Christ after the Resurrection.The feast is also called Whit Sunday, Whitsun, or Whit especially in the United Kingdom, where the following Monday was traditionally a holiday. Pentecost is celebrated seven weeks (50 days) after Easter Sunday, hence its name.Pentecost falls on the tenth day after Ascension Thursday.

Pentecost is historically and symbolically related to the Jewish harvest festival of Shavuot, which commemorates God giving the Ten Commandments at Mount Sinai fifty days after the Exodus. Among Christians, Pentecost commemorates the descent of the Holy Spirit upon the Apostles and other followers of Jesus as described in the New Testament Acts of the Apostles 2:1-31. For this reason, Pentecost is sometimes described as the "Birthday of the Church".

In other places, particularly Sicily and the Italian peninsula, rose petals were and are thrown from the galleries over the congregation calling to mind the tongues of fire. In modern times, this practice has been revived, and interestingly adapted as well, to include the strewing of origami doves from above, or suspending them – sometimes by the hundreds – from the ceiling. In some cases, red fans, or red handkerchiefs are distributed to the assembled worshippers to be waved during the procession, etc. Other congregations have incorporated the use of red balloons, signifying the “Church’s Birthday” into their festivities. These may be carried by worshippers, used to decorate the sanctuary, or released all at once.

Paul already in the 1st century notes the importance of this festival to the early Christian communities. (See: Acts 20:16 & Corinthians 16:8) Since the lifetime of some who may have been eye-whitnesses, annual celebrations of the descent of the Holy Spirit have been observed. Before the Second Vatican Council Pentecost Monday as well was a Holy Day of Obligation during which the Catholic Church addressed the newly baptized and confirmed. Since that time however Pentecost Monday is no longer solemnized.

"the promise of the Father about which you have heard me speak; for John baptized with water, but in a few days you will be baptized with the holy Spirit." When they had gathered together they asked him, "Lord, are you at this time going to restore the kingdom to Israel?" He answered them, "It is not for you to know the times or seasons that the Father has established by his own authority. But you will receive power when the holy Spirit comes upon you, and you will be my witnesses in Jerusalem, throughout Judea and Samaria, and to the ends of the earth." When he had said this, as they were looking on, he was lifted up, and a cloud took him from their sight. While they were looking intently at the sky as he was going, suddenly two men dressed in white garments stood beside them. They said, "Men of Galilee, why are you standing there looking at the sky? This Jesus who has been taken up from you into heaven will return in the same way as you have seen him going into heaven."

The Feast of the Ascension of Jesus is a Holy Day of Obligation.  Holy days of obligation are feast days on which Catholics are required to attend Mass and to avoid (to the extent that they are able) servile work.

The Ascension of Jesus is the Christian teaching found in the New Testament when the resurrected Jesus was taken up to heaven in his resurrected body,^{[Acts 1:9-11]} in the presence of eleven of his Apostles, occurring 40 days after the resurrection. Jesus ascended to his Father and his heavenly throne, and now sits at the right hand of God the Father in heaven. An angel told the watching disciples that Jesus' second coming would take place in the same manner as his ascension, that is, He would descend in bodily form. This is also described in other Biblical passages.

The Ascension of Jesus is professed in the Nicene Creed, which is spoken in the Christian liturgy, and in the West, by the Apostles' Creed. The Ascension implies Jesus' humanity being taken into heaven. The Feast of the Ascension, celebrated 40 days after Easter, is one of the chief feasts of the Christian year.