I just finished The Celtic Way of Evangelism by George Hunter. I'd highly recommend it. Hunter explains how Patrick and friends engaged the "barbarians" of Ireland, moving from what they already knew to what they had no clue about, the God of Scripture. Also significant is how the missionaries used community to evangelize the Irish. The people found belonging before believing. In other words, they were committed to the church and the community they experienced there before they were actually converted to Christ. Interesting about this short book is how much the missionary ways of Patrick, Aidan, and others sound like what is needed in today's postmodern times. Also striking is how the Roman church swooped down and killed the entire thing, because they didn't know how to handle aggressive, indigenous missional movements. If you are on the frontlines of mission, trying to engage postmoderns with the gospel, this historical study will be very helpful to you.