From publisher blurb: This supplement to the 1979 Game Master’s Guide – as originally authored by E. Gary Gygax and the worthy sages of TSR – provides several decades’ worth of comprehensive improvements, expansions, errata, clarifications, rulings, and interpretive aids for the Advanced rules set of the world’s foremost Fantasy Role-Playing Game. Supplementary notes, provided for particularly enterprising Game Masters, will also allow for conversion of concepts to the Essentials and 5th Edition rules sets.