Q. Why are the biblical books of Luke and Acts separated if they were written by the same person?
A. St. Luke did indeed write both these books, apparently as two volumes of the same work (see Acts 1:1; the Greek word translated here as “book” is logos and can be rendered in English as “book” or “volume”). The Gospel ends at the point where Acts begins, with the ascension of Our Lord into heaven (see Luke 24:50-53; Acts 1:1-2). So in a way it would make sense to arrange the New Testament books so that Acts immediately follows Luke.