From the back of the book:
What's a DM to do when the player characters in his campaign become so powerful that nothing in the world is a challenge for them anymore? Just what are the essential ingredients in an adventure geared toward high-level play?
Here is a trove of advice and new rules for every AD&D game Dungeon Master who wishes to create adventures for truly legendary heroes. Find everything you need to create encounters that confound the craftiest wizard and chill the most valiant warrior's heart. Discover the power of True Dweomers, the mightiest spells ever. Build new realities for your heroes to explore. Learn how to conduct magical duels and oversee the creation of magical items. Expand the horizons of your gaming experience with High-Level Campaigns.