Twelve Sporadic Groups

1. Background from General Group Theory.- 2. Assumed Results about Particular Groups.- 3. Codes.- 4. The Hexacode.- 5. The Golay Code.- 6. Subgroups of M24.- 7. The Ternary Golay Code and 2*M12.- 8. Lattices.- 9. The Leech Lattice and Conway Groups.- 10. Subgroups of the Conway Groups the Simple Groups of Higman-Sims, McLaughlin, Hall-Janko and Suzuki Local Subgroups Conjugacy Classes.- 11. Generation Three of the Happy Family and the Pariahs.- Appendix. Some Comments on the Atlas.- References.- List of Group Theoretic Notations.- The Orders of the Finite Simple Groups.