Acts: What is Demon Possession?

In Acts 19 severe spiritual battle breaks out, to the point that Jewish exorcists are physically attacked by a demon possessed man. What are we to make of all this? Was demon possession only in the past? Why was it so prevalent then but doesn't seem to be today? Can people be demon possessed today? Can Christians be? How can a person be delivered? Is this stuff still going on today? We will seek to tackle these issues through our study of the Bible.