The Acts of the Apostles (Koine Greek: Πράξεις Ἀποστόλων, Práxeis Apostólōn and Latin: Actūs Apostolōrum) is the fifth book of the New Testament. It recounts the founding of the Christian Church and the spread of its message across the Roman Empire.

Acts and the Gospel of Luke form a two-volume work known as Luke–Acts by the same author. Tradition identifies the writer as Luke the Evangelist, a doctor who travelled with Paul the Apostle, though the text is anonymous, not naming its author. Critical opinion near the end of the 20th century remained divided about whether Luke the physician wrote it. Many scholars still regard the author of Luke–Acts as a companion of Paul, although they note tensions with the authentic Pauline letters. Modern discussion treats Acts primarily as historiography while also considering genres such as novel, epic, and ancient biography, and scholars now focus more on the author's aims than on settling questions of strict historicity. Scholars usually date the book to 80–90 AD, and some propose 110–120 AD.

The first part of Luke–Acts, the Gospel of Luke, depicts how God fulfills the plan of salvation through the life, death, and resurrection of Jesus of Nazareth. Acts continues the story of Christianity in the 1st century, beginning with the ascension of Jesus and tracing the mission from Jerusalem into the wider Mediterranean world. The early chapters describe the Day of Pentecost, the shared life of the first believers, and the establishment of the church at Antioch. The later chapters follow Paul as he carries the message throughout the empire and conclude with his imprisonment in Rome as he awaits trial.

Luke–Acts addresses how the Jewish Messiah came to have an overwhelmingly non-Jewish church by arguing that the message reached the Gentiles after the Jewish rejection. The work also reads as a defense of the Jesus movement for Jewish audiences, since most speeches respond to Jewish concerns while Roman officials arbitrate disputes about Jewish customs and law. Luke presents the followers of Jesus as a Jewish sect entitled to legal protection, yet he remains ambivalent about the future of Jews and Christians, affirming Jesus' Jewish identity while emphasizing the Jews' rejection of the Messiah.

The name "Acts of the Apostles" was first used by Irenaeus in the late 2nd century. It is not known whether this was an existing name for the book or one invented by Irenaeus; it does seem clear that it was not given by the author, as the word práxeis (deeds, acts) only appears once in the text (Acts 19:18) and there it refers not to the apostles but to deeds confessed by their followers.

The Gospel of Luke and Acts make up a two-volume work which scholars call Luke–Acts. Together they account for 27.5% of the New Testament, the largest contribution attributed to a single author, providing the framework for both the Church's liturgical calendar and the historical outline into which later generations have fitted their idea of the story of Jesus and the early church. The author is not named in either volume. According to Church tradition dating from the 2nd century, the author was Luke, named as a companion of the apostle Paul in three of the letters attributed to Paul himself, but twentieth century scholarship cast this into doubt, with Theissen stating “a critical consensus emphasizes the countless contradictions between the account in Acts and the authentic Pauline letters." An example can be seen by comparing Acts' accounts of Paul's conversion (Acts 9:1–31, 22:6–21, and 26:9–23) with Paul's own statement that he remained unknown to Christians in Judea after that event (Galatians 1:17–24). The author "is an admirer of Paul, but does not share Paul's own view of himself as an apostle; his own theology is considerably different from Paul's on key points and does not represent Paul's own views accurately." Many modern scholars have therefore expressed doubt that the author of Luke–Acts was the physician Luke, and critical opinion on the subject was assessed to be roughly evenly divided near the end of the 20th century. More recent developments in interpretation find that the Paul and the author of Luke–Acts are not as different theologically as previously thought. Most scholars maintain that the author of Luke–Acts, whether named Luke or not, met Paul. He was educated, a man of means, probably urban, and someone who respected manual work, although not a worker himself; this is significant, because more high-brow writers of the time looked down on the artisans and small business people who made up the early church of Paul and were presumably Luke's audience.

The interpretation of the "we" passages as indicative that the writer was a historical eyewitness (whether Luke the evangelist or not), remains the most influential in current biblical studies. Objections to this viewpoint include the above claim that Luke–Acts contains differences in theology and historical narrative which are irreconcilable with the authentic letters of Paul the Apostle.

The earliest possible date for Luke–Acts is around 62 AD, the time of Paul's imprisonment in Rome, but most scholars date the work to 80–90 AD on the grounds that it uses Mark as a source, looks back on the destruction of Jerusalem, and does not show any awareness of the letters of Paul (which began circulating late in the first century). If it does show awareness of the Pauline epistles, and also of the work of the Jewish historian Josephus, as some believe, then a date in the early 2nd century is possible. However, many arguments mediate against this dating, such as the Gospel of John's awareness of the gospel, its independence from the Gospel of Matthew in the two-source hypothesis, and 1 Clement.