The Ascension of Jesus into Heaven is a biblical event narrated by both St. Mark and St. Luke.
St. Mark summarizes the event in a single verse.
The Catechism of the Catholic Church explains what happens at the Ascension of Jesus in more theological terms.
While Jesus' humanity may have ascended into Heaven, his abiding presence is still among us in a variety of ways, including his Real Presence in the consecrated Eucharistic bread and wine.
Catholics also believe that Jesus will come again at the end of time.