Wikipedia
Luke–Acts is the name usually given by biblical scholars to the composite work of the Gospel of Luke and the Acts of the Apostles in the New Testament. Together they describe the ministry of Jesus and the subsequent ministry of the apostles and the Apostolic Age.
Both the books of Luke and Acts are anonymous narratives written to a man named Theophilus. The book of Acts starts out with: "The former treatise have I made", probably referring to the Gospel of Luke. Almost all scholars believe that they were written by the same person referred to as Luke the Evangelist. Luke–Acts has sometimes been presented as a single book in published Bibles or New Testaments, for example, in The Original New Testament (1985) and The Books of the Bible (2007).
The traditional view holds that they were written by Luke named in Colossians , a physician and follower of Paul the Apostle, but some modern scholars reject that view. The work is Hellenized and written for a gentile audience. Marcion, a famous 2nd century heretic, who used a modified form of Luke known as the Gospel of Marcion, did not use Acts, perhaps he was unaware of it or intentionally excluded it from his biblical canon; Irenaeus, a proto-orthodox apologist, is the first to use and mention Acts, specifically against Marcionism.
Some scholars note that there are two versions of Luke-Acts with the non-canonical version 10-20 percent longer than the canonical version. Scholars disagree on which came first.