Acts 1 begins with Jesus' ascension into heaven, after working with his apostles for forty days. Before he departs, Jesus commissions the apostles to bear witness to him throughout the world. The apostles return to the upper room in Jerusalem, where they hold a prayer meeting with Jesus' family and other disciples, waiting for the promised Holy Spirit. In this chapter, the apostles replace Judas Iscariot, who kills himself after betraying Jesus. They recognize that they are beginning a new era in the history of Israel, and prepare for this by choosing Matthias as the twelfth apostle.