Zork was one of the first interactive fiction computer games and an early descendant of Colossal Cave Adventure. The first version of Zork was written in 1977–1979 on a DEC PDP-10 computer by Tim Anderson, Marc Blank, Bruce Daniels, and Dave Lebling, and implemented in the MDL programming language. All four were members of the MIT Dynamic Modelling Group.
Zork can run on modern Z-machine interpreters, as well as the older models it was made for originally.

"Zork" was originally MIT hacker jargon for an unfinished program. The implementors named the completed game Dungeon, but by that time the name Zork had already stuck. Zork has also been adapted to a widely panned book series.

Three of the original Zork programmers joined with others to found Infocom in 1979. That company adapted the PDP-10 Zork into Zork I-III, a trilogy of games for most popular small computers of the era, including the Apple II, the Commodore 64, the Atari 8-bit family, the TRS-80, CP/M systems and the IBM PC. Zork I was published on 5М" and 8" floppy disks. Joel Berez and Marc Blank developed a specialized virtual machine to run Zork I, called the Z-machine. The first "Z-machine Interpreter Program" ZIP for a small computer was written by Scott Cutler for the TRS-80. The trilogy was written in ZIL, which stands for "Zork Implementation Language", a language similar to LISP. Personal Software published what would become the first part of the trilogy under the name Zork when it was first released in 1980, but Infocom later handled the distribution of that game and their subsequent games. Part of the reason for splitting Zork into three different games was that, unlike the PDP systems the original ran on, micros did not have enough memory and disk storage to handle the entirety of the original game. In the process, more content was added to Zork to make each game stand on its own.

Zork is set in a sprawling underground labyrinth which occupies a portion of the "Great Underground Empire". The player is a nameless adventurer whose goal is to find the treasures hidden in the caves and return alive with them, ultimately inheriting the title of Dungeon Master. The dungeons are stocked with many novel creatures, objects and locations, among them grues, zorkmids, and Flood Control Dam #3—all of which are referenced by subsequent Infocom text adventures.

Zork and its relatives are works of interactive fiction. Zork distinguished itself in its genre as an especially rich game, in terms of both the quality of the storytelling and the sophistication of its text parser, which was not limited to simple verb-noun commands ("hit grue"), but some prepositions and conjunctions ("hit the grue with the Elvish sword").