Mirrodin is the name of the Magic: The Gathering expert-level block containing the Mirrodin (October 2, 2003, 306 cards), Darksteel (February 6, 2004, 165 cards) and Fifth Dawn (June 4, 2004, 165 cards) expansion sets. The Mirrodin expansion set, as well as the rest of the block, is centered on artifacts and was only the second set to do so (from a card frequency point of view) since Antiquities. The percentage of artifact cards is much higher than in any preceding set. Each of the expansion symbols in the Mirrodin block depicts a legendary artifact: Sword of Kaldra (Mirrodin), Shield of Kaldra (Darksteel) and Helm of Kaldra (Fifth Dawn).

The setting for Mirrodin is a plane by the same name. An artificial world created by the planeswalker Karn, originally named Argentum, and named after the Mirari by Memnarch, Mirrodin's environments and inhabitants mix organic and metallic. Mirrodin is orbited by four satellites, which are called suns and moons interchangeably, that correspond to red, black, white and blue magic. Green was notably absent until Glissa Sunseeker became a conduit for its birth.

The set focuses on five main regions on Mirrodin, each corresponding to a part of the Magic color pie:

The main character of the story is the elf Glissa Sunseeker, who visits all these places, guided by revenge against the machines that killed her family. The story is captured in the novel The Moons of Mirrodin by Will McDermott. Magic returned to the setting of Mirrodin with the Scars of Mirrodin block.

The Darksteel Eye is the second novel in the Mirrodin Cycle by Jess Lebow. It continues the journey of Glissa, after the infiltration of the Synod and the recollection of all the golem Bosh's memories. They now must travel back across Mirrodin to seek the power that resides in the center of Mirrodin.

The final book in this expansion series is named The Fifth Dawn. In the story, Glissa, Bosh, and Slobad journey deep within Mirrodin's core to confront the insidious Memnarch. With them is the Kaldra avatar—an immensely powerful being of energy summoned when Kaldra's sword, shield, and helm were brought together. But what was supposed to be the world's salvation turns out to be a vile trick. With a single spell, Memnarch seizes the avatar and turns it on Glissa and her companions. Kaldra's avatar relentlessly pursues Glissa into the Tangle, destroying everything in its way. Finally, at the Radix, Glissa's destiny becomes clear. As rage and despair overcome her, Glissa's body calls forth a great column of green mana from Mirrodin's core, annihilating the avatar in the process. Now that mana hangs overhead in a glowing sphere—the green sun at last, Mirrodin's fifth dawn.

Mirrodin is notable for being the first expansion set to feature the new card front design (which debuted in 8th Edition). The high number of artifacts in Mirrodin highlighted the inherent flaw of the new border design — artifact cards, which were now bordered in a very light grey instead of brown, were very hard to distinguish from white cards. The problem prompted Wizards of the Coast to change the bordering background of artifact cards to a much darker grey in Fifth Dawn. Also due to complications when switching to the new card frame, mana symbols in the text box of Mirrodin cards are greyed out instead of being in color. Beginning with Mirrodin Wizards reduced the size of their large expansion sets from 350 to 306 cards. This was due to regular complaints, that Wizards was producing too many cards and players could not keep up. Beginning with Darksteel Wizards also increased the size of small expansion sets from 143 to 165 cards. Thus the number of cards released each year would stay the same, but then Magic developer Randy Buehler explained that Wizards believed this change would make it easier for collectors and players to keep up with the number of new cards as these would be released more homogeneously over the course of the year.

Darksteel was the first "small" expansion to have 165 cards, whereas previous small expansions had 143, (with the exception of Legions which had 145 as a balance among the five colors.)