Eldritch Wizardry was the third supplement to TSR's original 3-booklet Dungeons & Dragons game (variously referred to as the Original D&D Set, the White Box Edition or the Original Collectors Edition). Eldritch Wizardry was published in 1976. It was written by Gary Gygax and Brian Blume.

Eldritch Wizardry extended the D&D game into the realm of ultra high level adventuring. It dealt with demons, devils, and magical artifacts. Many of the artifacts that appeared in the AD&D Dungeon Master's Guide first appeared in Eldritch Wizardry, although in a different form. For example, the original Sword of Kas was a +3 sword (+5 against undead and demons).

It also introduced the druid character class which surprisingly remained unchanged when re-introduced into AD&D via the Players Handbook.

What probably caused gamers the most consternation was not the booklet's color cover painting of a naked woman chained to an altar but Eldritch Wizardry's introduction of psionics. The system, which didn't exactly hum in the later first edition AD&D, was utterly cumbersome and entirely arbitrary as laid out in supplement three. Only humans could be psionic. Druids and monks could not be psionic. Psionic characters had certain character class bonuses stripped. For example a psionic "fighting man" character lost hit points, magic users lost spells, and clerics turned undead at a lower level.

The first four printings of Eldritch Wizardry also provided additional proof that D&D owed more to The Lord of the Rings than Gygax liked to let on (Gygax, I believe, claimed he found The Lord of the Rings boring and any similarities were purely coincidental.) Much in the same way early editions of D&D referred to Halflings as "hobbits" until the Tolkien estate threatened a lawsuit, Eldritch Wizardry makes a reference to a "balrog". (The balrog was snuck into AD&D via the Monster Manual. It was called the "Type VI demon" aka Balor.)

See also for additional supplements:

I - Greyhawk, II - Blackmoor, IV - Gods, Demi-Gods & Heroes, V - Swords & Spells