Johannes Munck, editor of the Anchor Bible volume on Acts, writes, “It has been considered reasonable to assume that Acts was written by a fellow worker of Paul, a Gentile Christian, and a physician” (p. xxix). This assumption is based on internal evidence in the Acts of the Apostles, although it is not universally embraced.
That the author was Paul’s companion is strongly supported by the author’s use of “we” throughout the text, and his familiarity with Paul’s ministry to Gentiles suggests he was a Gentile himself. The use of medical terms may reflect professional training, but this is inconclusive. What is probably most compelling in determining the identity of the author of Acts is the argument from tradition. From A.D. 150 the Church has accepted St. Luke as the author of both the Gospel attributed to him and the Acts of the Apostles.
The similarities between the two texts (they comprise one-quarter of the New Testament) are unmistakable: They are the most self-consciously literary of all the New Testament writings, and the Acts of the Apostles is a precious heritage, providing a history of the Church’s earliest activity.