This is the third iteration of the classic D&D rules set. This single book runs D&D characters from levels 1-36 via the original Basic, Expert, Companion, and Masters rules. Also includes background on Mystara and Hollow World.

From the back cover:

Whether you're a player or a Dungeon Master, the DUNGEONS & DRAGONS Rules Cyclopedia is now the comprehensive sourcebook you need for the original fantasy role-playing game! For ages 12 and up, the Cyclopedia contains the complete game system and hundred of features, including:

• All the rules from the D&D boxed set series, including Basic, Expert, Companion, and Masters.
  
• Guidelines to develop and play characters from levels 1–36.
  
• Comprehensive lists of weaponry and equipment.
  
• Expansion rules including optional skills and talents.
  
• An overview of the Known World and HOLLOW WORLD game settings, the official D&D campaign world; and Rules to convert D&D games and characters into AD&D 2nd Edition game statistics and back again.
  
  Fully compatible with the new DUNGEONS & DRAGONS Boxed Set, this volume allows players the full scope of fantasy role-playing from the dungeons to the Outer Planes. Now, more than ever, the DUNGEONS & DRAGONS game is ready and waiting for you!