Master DM's Book: Anti-Magic Effects

The D&D Master Set provides an in-depth explanation of anti-magic effects, described previously in the 6th level magic-user spell "Anti-Magic Shell" and scroll of protection from magic in the D&D Expert Set, and a beholder's "anti-magic ray" in the D&D Companion Set.

Illustration by Terry Dykstra, from the D&D Rules Cyclopedia (1991)

The concept of "magic resistance" was introduced in the AD&D 1e Monster Manual:

MAGIC RESISTANCE indicates the percentage chance of any spell absolutely failing in the monster’s presence.  It is based on the spell being cast by a magic-user of 11th level, and it must be adjusted upwards by 5% for each level below 11th or downwards for each level above 11th of the magic-user casting the spell.  Thus a magic resistance of 95% means that a 10th level magic-user has no possibility of affecting the monster with a spell, while a 12th level magic-user has a 10% chance.  Even if a spell does take effect on a magic-resistant creature, the creature is entitled to normal saving throws.  Note also that the magic resistance of a creature has an effect on certain existing spells such as hold portal, where it indicates the probability of the magic resistance shattering the existing spell.

AD&D 1e Monster Manual (1977)

Why Anti-Magic Exists:

A rationale for anti-magic in BECMI is given:

Anti-Magic results from differences between life forms native to different planes of existence.  Magic native to the Inner Planes of existence (the Prime, Ethereal, and Elemental planes) functions best when used on creatures and things native to those planes.  Creatures from other planes are not made the same way.

All creatures native to the Inner Planes are made of components of the four Spheres of Power (Matter, Energy, Time, and Thought) and are all governed by the Sphere of Entropy (or Death).  But creatures of the Astral and Outer Planes lack one or more of the four components, and may avoid most of the effects of Death as well.

Master DMs Book

Examples of how anti-magic disrupts potions, personal spell effects, and area spell effects are provided.