Edition: Fount, 1982 (Buy from Amazon)
Review number: 987
After the Narnia series and possibly his science fiction trilogy, The Screwtape Letters is Lewis' best known work. It isn't intended, like most of his fiction, as an apologetic for Christianity, but as an aid to a Christian - it is designed to help someone overcome temptation. This purpose is carried out in such a way that it is entertaining even to a non-Christian.
The reason for this is partly the method used, the conceit that the contents are letters addressed by a senior devil to a more junior, inexperienced tempter, and partly that the whole book is very well written and clearly thought out. If the theological background is accepted, even for a moment, then the letters are convincing; if not, then they are certainly entertaining and occasionally thought provoking.