""An excellent introduction to this area for anyone who is looking for an informal survey... written in a lively and readable style."" R.E. Boucherds, University of California at Berkeley for the Bulletin of the AMS ""Gannon wants to explain to us ""what is really going on."" His book is like a conversation at the blackboard, with ideas being explained in informal terms, proofs being sketched, and unknowns being explored. Given the complexity and breadth of this material, this is exactly the right approach. The result is informal, inviting, and fascinating."" Fernando Q. Gouvea, MAA Reviews ""It is written in a breezy, informal style which eschews the familiar Lemma-Theorem-Remark style in favor of a more relaxed and continuous narrative which allows a wide range of material to be included. Gannon has written an attractive and fun introduction to what is an attractive and fun area of research."" Geoffrey Mason, Mathematical Reviews