In video games, an open world is a virtual world in which the player can approach objectives freely, as opposed to a world with more linear and structured gameplay. Notable games in this category include Grand Theft Auto: San Andreas (2004), Red Dead Redemption 2 (2018), and Minecraft (2011).

Games with open or free-roaming worlds typically lack level structures like walls and locked doors, or the invisible walls in more open areas that prevent the player from venturing beyond them; only at the bounds of an open-world game will players be limited by geographic features like vast oceans or impassable mountains. Players typically do not encounter loading screens common in linear level designs when moving about the game world, with the open-world game using strategic storage and memory techniques to load the game world dynamically and seamlessly. Open-world games still enforce many restrictions in the game environment, either because of absolute technical limitations or in-game limitations imposed by a game's linearity.

While the openness of the game world is an important facet to games featuring open worlds, the main draw of open-world games is about providing the player with autonomy—not so much the freedom to do anything they want in the game (which is nearly impossible with current computing technology), but the ability to choose how to approach the game and its challenges in the order and manner as the player desires while still constrained by gameplay rules. Examples of high level of autonomy in computer games can be found in massively multiplayer online role-playing games (MMORPG) or in single-player games adhering to the open-world concept such as the Fallout series. The main appeal of open-world gameplay is that it provides a simulated reality and allows players to develop their character and its behavior in the direction and pace of their own choosing. In these cases, there is often no concrete goal or end to the game, although there may be the main storyline, such as with games like The Elder Scrolls V: Skyrim.

An open world is a level or game designed as nonlinear, open areas with many ways to reach an objective. Some games are designed with both traditional and open-world levels. An open world facilitates greater exploration than a series of smaller levels, or a level with more linear challenges. Reviewers have judged the quality of an open world based on whether there are interesting ways for the player to interact with the broader level when they ignore their main objective. Some games actually use real settings to model an open world, such as New York City.

A major design challenge is to balance the freedom of an open world with the structure of a dramatic storyline. Since players may perform actions that the game designer did not expect, the game's writers must find creative ways to impose a storyline on the player without interfering with their freedom. As such, games with open worlds will sometimes break the game's story into a series of missions, or have a much simpler storyline altogether. Other games instead offer side-missions to the player that do not disrupt the main storyline. Most open-world games make the character a blank slate that players can project their own thoughts onto, although several games such as Landstalker: The Treasures of King Nole offer more character development and dialogue. Writing in 2005, David Braben described the narrative structure of current video games as "little different to the stories of those Harold Lloyd films of the 1920s", and considered genuinely open-ended stories to be the "Holy Grail" for the fifth generation of gaming. Gameplay designer Manveer Heir, who worked on Mass Effect 3 and Mass Effect: Andromeda for Electronic Arts, said that there are difficulties in the design of an open-world game since it is difficult to predict how players will approach solving gameplay challenges offered by a design, in contrast to a linear progression, and needs to be a factor in the game's development from its onset. Heir opined that some of the critical failings of Andromeda were due to the open world being added late in development.

Some open-world games, to guide the player towards major story events, do not provide the world's entire map at the start of the game, but require the player to complete a task to obtain part of that map, often identifying missions and points of interest when they view the map. This has been derogatorily referred to as "Ubisoft towers", as this mechanic was promoted in Ubisoft's Assassin's Creed series (the player climbing a large tower as to observe the landscape around it and identify waypoints nearby) and reused in other Ubisoft games, including Far Cry, Might & Magic X: Legacy and Watch Dogs. Other games that use this approach include Middle-earth: Shadow of Mordor, The Legend of Zelda: Breath of the Wild, and Marvel's Spider-Man. Rockstar games like GTA: San Andreas and GTA IV series lock out sections of the map as "barricaded by law enforcement" until a specific point in the story has been reached.

Games with open worlds typically give players infinite lives or continues, although some force the player to start from the beginning should they die too many times. There is also a risk that players may get lost as they explore an open world; thus designers sometimes try to break the open world into manageable sections. The scope of open-world games requires the developer to fully detail every possible section of the world the player may be able to access, unless methods like procedural generation are used. The design process, due to its scale, may leave numerous game world glitches, bugs, incomplete sections, or other irregularities that players may find and potentially take advantage of. The term "open world jank" has been used to apply to games where the incorporation of the open world gameplay elements may be poor, incomplete, or unnecessary to the game itself such that these glitches and bugs become more apparent, though are generally not game-breaking, such as the case for No Man's Sky near its launch.

The mechanics of open-world games are often overlapped with ideas of sandbox games, but these are considered different concepts. Whereas open world refers to the lack of limits for the player's exploration of the game's world, sandbox games are based on the ability of giving the player tools for creative freedom within the game to approach objectives, if such objectives are present.