All the miscellaneous magical items from the D&D Basic, Expert and Companion sets plus 500 new items. Choices range from the useful (Cleats of Gripping) to the silly (Armchair of Ugliness).
From the back cover:
"Tell me, teacher - How does one open the cabinet of security? Of what use is the banner of bravery? And what are the limits of the sun deck? My books and scrolls tell me nothing about many of the magical treasures I've heard you mention time and again."
"No, Paedras, your manuscripts are too general. But since you have inquired, I will allow you to peruse this, one of my most treasured volumes - The Book of Marvelous Magic. It will answer your questions."
And now you, too, can learn the secrets that were revealed to Phaedras! The Book of Marvelous Magic is the ultimate sourcebook on magical items and their twists and quirks. Over 500 new magical items are described in detail. An appendix describes how these items can be used with the AD&D game."