The Acts of the Apostles , usually referred to simply as Acts, is the fifth book of the New Testament

New Testament

The New Testament is the second major division of the Christian biblical canon, the first such division being the much longer Old Testament....

; Acts outlines the history of the Apostolic Age

Apostolic Age

The Apostolic Age of the history of Christianity is traditionally the period of the Twelve Apostles, dating from the Crucifixion of Jesus and the Great Commission in Jerusalem until the death of John the Apostle in Anatolia...

. The author is traditionally identified as Luke the Evangelist

Luke the Evangelist

Luke the Evangelist was an Early Christian writer whom Church Fathers such as Jerome and Eusebius said was the author of the Gospel of Luke and the Acts of the Apostles...

; see Authorship of Luke-Acts

Authorship of Luke-Acts

The authorship of the Gospel of Luke and the Acts of the Apostles is an important issue for biblical exegetes who are attempting to produce critical scholarship on the origins of the New Testament...

 for details.
While the precise identity of the author is debated, the consensus is that this work was composed by a (Koine) Greek speaking Gentile writing for an audience of Gentile Christians.
The Early Church Fathers

Church Fathers

The Church Fathers, Early Church Fathers, Christian Fathers, or Fathers of the Church were early and influential theologians, eminent Christian teachers and great bishops. Their scholarly works were used as a precedent for centuries to come...

 wrote that Luke was a physician in Antioch and an adherent of the Apostle Paul.