Adventure is a 1980 action-adventure game developed by Warren Robinett and published by Atari, Inc. for the Atari 2600. The player controls a square avatar whose quest is to explore an open-ended environment to find a magical chalice and return it to the Golden Castle. The game world is populated by roaming enemies: three dragons that can eat the avatar and a bat that randomly steals and moves items around the game world. Adventure introduced new elements to console games, including enemies that continue to move when offscreen.

The game was conceived as a graphical version of the 1977 text adventure Colossal Cave Adventure. Robinett spent approximately a year designing and coding the game while overcoming a variety of technical limitations of the console's hardware, as well as difficulties with Atari management. As a result of conflicts with Atari's management which denied giving public credit for programmers, Robinett programmed a secret room within the game that contained his name; this room was only found by players after the game was shipped and Robinett had left Atari. While not the first such Easter egg, Robinett's secret room pioneered this idea within video games and other forms of media, and it since has become a part of popular culture, such as in the climax of Ernest Cline's 2011 novel Ready Player One and its 2018 film adaptation.

Adventure received positive reviews at the time of its release and in the decades since; it is often named as one of the industry's most influential games and among the greatest video games of all time. It is one of the first action-adventure and fantasy games, and inspired other games in the genre. More than a million copies of Adventure were sold, and the game has been included in numerous Atari game collections for modern computer hardware. The game's prototype code was used as the basis for the 1979 Superman game, and a planned sequel eventually formed the basis for the Swordquest games.

In Adventure, the player's goal is to recover the Enchanted Chalice, which an evil magician has stolen and hidden in the kingdom, and return it to the Golden Castle. The kingdom is made of a total of 30 rooms, with various obstacles, enemies, and mazes located in and around the Golden, White, and Black Castles. The kingdom is guarded by three dragons—the yellow Yorgle, the green Grundle, and the red Rhindle—that protect or flee from various items and attack the player's avatar. A hostile bat can roam the kingdom freely, carrying an item or a dragon around; the bat was to be named "Knubberrub" but the name is not in the manual. The bat's two states are agitation and non-agitation. When in the agitated state, the bat will either pick up or swap what it currently carries with an object in the present room, eventually returning to the non-agitated state where it will not pick up an object. The bat continues to fly around, swapping objects, even offscreen.

The player's avatar is a square that can move within and between rooms; each room is represented by a single screen. Helpful objects include keys that open the castles, a magnet that pulls items towards the player, a magic bridge that the player can use to cross certain obstacles, and a sword which can be used to defeat the dragons. The player may only carry one object at a time. If eaten by a dragon, the player can then opt to resurrect the dead avatar instead of completely restarting the game. The avatar reappears at the Golden Castle and all objects remain at their latest location, but all slain dragons are resurrected. The ability to resurrect the avatar without resetting the entire game is one of the earliest examples of a "continue game" option in video games.

The game offers three different skill levels. Level 1 is the easiest, as it uses a simplified room layout and does not include the White Castle, bat, red dragon, or invisible mazes. Level 2 is the full version of the game, with the various objects appearing in set positions at the start. Level 3 is similar to Level 2, but the location of the objects is randomized for a greater challenge. The player can use the difficulty switches on the Atari 2600 to further control the game's difficulty; one switch controls the dragons' bite speed, and one causes them to flee when the player carries the sword.

Adventure was designed and programmed by Atari employee Warren Robinett and published by Atari, Inc. At the time, Atari programmers were generally given full control on the creative direction and development cycle for their games; to stay productive, this required them to begin planning their next game as they neared completion of their current one. Robinett was finishing his work on Slot Racers when he was given an opportunity to visit the Stanford Artificial Intelligence Laboratory by Julius Smith, one of several friends he was sharing a house with. There, he was introduced to the 1977 version of the computer text game Colossal Cave Adventure, created by Will Crowther and modified by Don Woods. After playing the game for several hours, he was inspired to create a graphical version.

Robinett began designing his graphics-based game with the help of a Hewlett-Packard 1611A logic analyzer (a debugging tool) around May to June 1978. He was soon aware that memory use was critical because Atari 2600 cartridge ROMs had only 4096 bytes (4 KB), and the system had 128 bytes of RAM for program variables. In contrast, Colossal Cave Adventure used hundreds of kilobytes of memory on a large computer. The final game used nearly all of the available memory (including 5% of the cartridge storage for Robinett's Easter egg), with 15 unused bytes from the ROM capacity. Robinett credits Ken Thompson, his professor at University of California, Berkeley, with teaching him the skills needed to use the limited memory efficiently. Thompson had required his students to learn the C programming language that he had invented at AT&T, and Robinett carried C techniques into assembly language.