Twelve sporadic groups

This text provides an extensive,leisurely and rigorous treatment of the twelve sporadic simple groups which form the first two generations of the Happy Family. The author's treatment of coding and lattice theory starts with basic definitions and goes far enough to prove suitable existence and uniqueness theorems for the Golay code and Leech lattice. Furthermore, full definitions and elementary arguments are given most of the time. The text is meant to be sensitive to beginners, like graduate students with some background in finite group theory, mathematicians in other fields and mathematical physicists.