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 2ยทM12 -- 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