A game demo is an often, but not always, freely distributed demonstration or preview of an upcoming or recently released computer or video game.

Demos are typically released by the game's publisher to help consumers get a feel of the game before deciding whether to buy the full version. For console video games, they are often released with magazines that include the demos on a CD or DVD and likewise may be exclusive to a certain publication. Demos are also sometimes released on cover tape/disks, especially in the United Kingdom and mainland Europe, but given the increasing size of demos and widespread availability of broadband internet, this common practice throughout the 1980s and '90s gradually lost cover focus to full games. With the advent of console online services such as Xbox Live or Playstation Network, demos are also becoming available as a free or premium downloadFact: date=August 2008.

Console manufacturers also often release their systems with a demo disc containing playable previews of games to be released for their console.

Distribution

In the early 1990s, shareware distribution was a popular method of publishing games for smaller developers, including then-fledgling companies such as Apogee Software (now 3D Realms), Epic Megagames (now Epic Games), and id Software. It gave consumers the chance to try a trial portion of the game, usually restricted to the game's complete first section or "episode", before purchasing the rest of the adventure. Racks of games on single 5 1/4" and later 3.5" floppy disks were common in many stores, often very cheaply. Since the shareware versions were essentially free, the cost only needed to cover the disk and minimal packaging. Sometimes, the demo disks were packaged within the box of another game by the same company. As the increasing size of games in the mid-90s made them impractical to fit on floppies, and retail publishers and developers began to earnestly mimic the practice, shareware games were replaced by shorter demos that were either distributed free on CDs with gaming magazines or as free downloads over the Internet, in some cases becoming exclusive content for specific websites.

Shareware was also the distribution method of choice of early modern first-person shooters (FPS) like Wolfenstein 3D and Doom.

There is a technical difference between shareware and demos. Up to the early 1990s, shareware could easily be upgraded to the full version by adding the "other episodes" or full portion of the game; this would leave the existing shareware files intact. Demos are different in that they are "self-contained" programs which are not upgradable to the full version. A good example is the Descent shareware versus the Descent II demo; players were able to retain their saved games on the former but not the latter.

Medium

The availability of demos varies between formats. Systems that use cartridges have typically not had demos available to them, due to the cost of duplication, whereas systems supporting more cheaply produced media, such as tapes, floppy disks, and later CD-ROM and DVD-ROM have; the Internet has more recently been a source for demos, although typically this is in addition to other distribution media available for the system in question. Also the Xbox Live as well as other gaming services have demos available for download 24/7.