A nice book on the ideas that sparked the first crusade and emerged from it, from the pope's motivations to the ideas of lay crusaders and the subsequent interpretations of contemporary theologians and historians. The title describes the book well and the author goes through a nice selection of citations from contemporary sources. This is an excellent source if you're interested in the ideology behind the crusades, but not so useful if you're looking for a narrative of the first crusade. In any event it certainly fulfilled my expectations and I wish it had extended to the next crusades as well.