The same author who wrote the Gospel of Luke. We know him as Luke, a Greek physician and traveling companion of the apostle Paul. Acts is quite literally Volume 2 of his report. He says so in the very first sentence:

So the "former book" is the Gospel of Luke, a carefully researched biography of Jesus. Acts picks up the story on the exact day Luke's Gospel ends—the day Jesus ascends into heaven—and follows the explosive growth of the movement for the next 30 years.

And here's the part that often surprises skeptics: Luke wasn't just a historian compiling second-hand stories. He was there for significant portions of the book. As you read, you’ll notice the narration suddenly switch from "they" to "we," beginning in Acts 16:10. This isn't a grammatical error. This is Luke, a meticulous historian in the Greco-Roman tradition, quietly signaling: I was on this boat. I was in that prison. I witnessed this with my own eyes.

Most scholars date the completion of Acts somewhere between AD 62 and 85. There's a compelling argument for the earlier date: the book ends abruptly with the apostle Paul alive and under house arrest in Rome, awaiting trial before Caesar. The narrative never mentions Paul's eventual execution (c. AD 64-67), Peter's death (c. AD 64), or the catastrophic destruction of the Jerusalem temple by the Romans (AD 70). These were arguably the three biggest events in early Christian history. A historian writing after these events would almost certainly have included them as the climax of the story. The fact that Luke doesn't suggests he was writing before they happened.

Why write it? It's addressed to the same man as the Gospel, "Theophilus" (likely a high-ranking Roman official), and for a similar purpose: so that you may know the certainty of the things you have been taught. But the focus shifts. The Gospel was about proving who Jesus was. Acts is about proving the power and legitimacy of the movement He started. It's a careful, orderly account showing that this new faith isn't a political threat, but the fulfillment of God’s ancient promises.

This is the critical question. Is Acts a reliable history or a faith-based fiction? Consider the evidence:

1. The author is partly an eyewitness. The "we" passages (Acts 16, 20, 21, 27, 28) put Luke directly inside the action. The account of the shipwreck on Malta in chapter 27 is so filled with precise, technical details of first-century seamanship and Mediterranean weather patterns that it’s considered by classical historians a masterpiece of ancient maritime reporting.

2. The history checks out at a microscopic level. Luke names 32 countries, 54 cities, and 95 individuals (many of them outside the Christian movement). Crucially, he gets the specific, often obscure, titles of local officials correct in every region — proconsuls in senatorial provinces like Achaia, "politarchs" in Thessalonica, an Asiarch in Ephesus, a "praetor" in the Roman colony of Philippi. These titles varied from province to province and changed over time. For one author to get them all correct is a stunning display of historical precision. The famous archaeologist Sir William Ramsay, initially a skeptic, set out to disprove Luke's account but was converted after his research continually verified Luke's accuracy at every turn.

3. He records embarrassing things. A PR piece or propaganda would scrub the internal failures. Luke includes them. He shows Christian leaders in sharp public disagreement (Paul and Barnabas splitting up). He records Peter, the head apostle, being publicly corrected for hypocrisy. He tells of a prominent couple dropping dead after lying to the group about money. Believers are beaten, imprisoned, and killed. This isn't a sanitized story of success; it's a gritty, honest account of a messy, struggling, and very human movement. This commitment to truth over image reveals something essential about its author and the events he's recording.

4. The growth he describes is independently confirmed. About 50 years after Acts was likely written, the Roman governor Pliny the Younger writes a panicked letter to the emperor Trajan (c. AD 112). He’s confused. This "Christian" thing has spread so rapidly in his province that the pagan temples are emptying out. He doesn't know what to do with them—they seem to be moral people, but they stubbornly refuse to worship the emperor. Pliny, a hostile witness, accidentally confirms the two central claims of Acts: that the movement experienced explosive, unexplainable growth, and that its followers placed their allegiance in Jesus above all earthly power.

Acts moves quickly through cities and across the Roman world. Don't get bogged down in the geography. Instead, watch for the repeating pattern: ordinary people, with no political power, no financial backing, and no army, are filled with a strange new courage. They refuse to be silent about what they saw, and as a result, the movement spreads like wildfire, crossing every social, racial, and economic barrier. That's the pattern. The central question of Acts is, what is the *source* of that power?