"Planescape" is an expansion of ideas presented in the "Advanced Dungeons & Dragons" "Dungeon Master's Guide" (First Edition) and the original "Manual of the Planes". When "Advanced Dungeons & Dragons" 2nd edition was published, a decision was made not to include angelic or demonic creatures, and so the cosmology was largely ignored. However, fan demand for a 2nd Edition "Manual of the Planes" was strong enough to justify its expansion into a full-fledged campaign setting, and so in 1994 Planescape was released.