The -> CHURCH is called apostolic because she was founded upon the apostles, holds fast to their Tradition, and is governed by their successors. [857-860, 869, 877]
Jesus called the -> APOSTLES to be his closest collaborators. They were his eyewitnesses. After his Resurrection, he appeared to them repeatedly. He bestowed on them the Holy Spirit and sent them as his authoritative messengers to all the world. They assured unity in the early Church. They conferred their mission and authority upon their successors, the bishops, through the laying on of hands. This process is called -> APOSTOLIC SUCCESSION.