Fallout (also known as Fallout: A Post Nuclear Role Playing Game) is a 1997 role-playing video game developed and published by Interplay Productions, set in a mid-22nd century post-apocalyptic and retro-futuristic world, decades after a global nuclear war led by the United States and China. Fallout's protagonist, the Vault Dweller, inhabits an underground nuclear shelter. The player must scour the surrounding wasteland for a computer chip that can fix the Vault's failed water supply system. They interact with other survivors, some of whom give them quests, and engage in turn-based combat.

Tim Cain began working on Fallout in 1994. It began and was conceptualized as based on the role-playing game GURPS, but after Steve Jackson Games objected to Fallout's violence, Cain and designer Christopher Taylor created a new character customization scheme, SPECIAL. Interplay initially gave the game little attention, but eventually spent $3 million and employed up to thirty people to develop it. Interplay considered Fallout the spiritual successor to its 1988 role-playing game Wasteland and drew artistic inspiration from 1950s literature and media emblematic of the Atomic Age as well as the films Mad Max and A Boy and His Dog. The quests were intentionally made morally ambiguous. After three and a half years of development, Fallout was released in North America in October 1997.

Fallout received acclaim for its open-ended gameplay, character system, plot, and setting. It won "Role-Playing Game of the Year" from GameSpot and Computer Games Magazine and was nominated by the Academy of Interactive Arts & Sciences at the Spotlight Awards. Fallout was a commercial success, selling more than half a million copies worldwide. Often listed among the greatest video games of all time, Fallout has been credited for renewing consumer interest in the role-playing video game genre. It spawned the widely successful Fallout series, the rights to which were purchased in 2007 by Bethesda Softworks.

Fallout is a role-playing video game. The player begins by selecting one of three characters, or one with player-customized attributes. The protagonist, known as the Vault Dweller, has seven primary statistics that the player can set: strength, perception, endurance, charisma, intelligence, agility, and luck. Each statistic may range from one to ten, provided their sum does not exceed 40. Two other statistics set during character creation are skills and traits. All 18 skills are learned abilities, their effectiveness determined by a percentage value. Their initial effectivenesses are determined by the primary statistics, but three can be tagged and given a 20% boost. Traits are character qualities with both a positive and negative effect; the player can pick up to two from a list of sixteen. During gameplay, the player can gather experience points through various actions. For gathering experience points, the player will level up and may increase their skills by a set number of points. Every three (or four with the Skilled trait) levels, the player can grant themself a special ability, known as perks. There are 48 perks (plus two extra perks which can only be obtained by wearing certain types of armor) and each has prerequisites that must be met. For example, "Animal Friend", which prevents animals from attacking the player character, requires the player to be level nine, have an intelligence of five, and have an outdoorsman skill of 25%.

In Fallout, the player explores the game world from a trimetric perspective and interacts with non-player characters (NPCs). Characters vary in their amount of dialogue; some say short messages, while others speak at length. Significant characters are illustrated with 3D models, known as "talking heads", during conversations. The player can barter with other characters or buy goods using bottle caps as currency. The game has companions that the player can recruit for exploration and combat, although they cannot be directly controlled.

There are three main quests where completion is required, two of them given after completion of the first one. The first main quest has a time limit of 150 in-game days; the game ends if the player fails to complete it within the allotted time. Some characters give the player side quests; if the player solves them, they receive experience points and occasionally a reward in the form of money and/or goods. The player can utilize the PIP-Boy 2000, a portable wearable computer that tracks these quests. Many quests feature multiple solutions; they can often be completed through diplomacy, combat, or stealth, and some allow solutions that are unconventional or contrary to the original task. Based on how they completed quests, the player can earn or lose reputation points, which determine how others treat them. The player's actions dictate what future story or gameplay opportunities are available and the ending.

Combat is turn based and uses an action-point system, the number of action points that are available depending on certain perks and the player's allocation in the agility statistic. During each turn, multiple actions may be performed by the player until they run out of action points. Different actions such as attacking, moving, reloading, interacting with objects mid-combat, and accessing the inventory consume different amounts of points. The player can rapidly switch between two equipped weapons, and may acquire a diverse range of weapons, many of which can target specific areas of enemies. Melee (hand-to-hand) weapons typically have two attacks: swing or thrust. If the player has equipped no weapon, they can punch or kick.

On October 23, 2077, a worldwide nuclear war between the United States and China following a global conflict caused by resource shortages devastated the world and destroyed modern civilization. The events of Fallout take place nearly a century later in 2161, and follow the Vault Dweller, a human born and raised within Vault 13, one of a number of high-tech underground fallout shelters built to protect survivors. Those on the surface live off the salvage of the old world.