Old-School Essentials is a modular game where the core rules of the game are extended by additional "rules modules" which add content for different genres of fantastic adventure. The Old-School Essentials Rules Tome is a compilation of the core rules plus four rules modules, forming a complete game for Classic Fantasy adventures:

The Player's Tome. Cover art by Peter Mullen. Details in gold foil. 248 pages, A5 (Digest-sized). Old-School Essentials Advanced Fantasy book 1 of 2. The Player's Tome contains the complete game rules, a massive selection of character classes and races, hundreds of spells, and full lists of equipment, mounts, vehicles, and hirelings. Everything a player needs.