Gameplay in Fallout centers around the game world, visiting locations and interacting with the local inhabitants. Occasionally, inhabitants will be immersed in dilemmas, which the player may choose to solve in order to acquire karma and experience points. Fallout deviates from most role-playing video games in that it often allows the player to complete tasks in multiple ways, allowing solutions that are unconventional or contrary to the original task, in which case the player may still be rewarded, or earn an unconventional reward. The player's actions and/or inaction dictates what future story or gameplay opportunities are available, and ultimately dictates the ending of the game. Players will encounter hostile opponents and – if such encounters are not avoided using stealth or persuasion – they and the player will engage in turn-based combat. Excepting conversations with non-player characters, non-combat portions of the game are played in real time.
Combat in Fallout is turn-based. The game uses an action-point system, wherein each turn, multiple actions may be performed by each character until all points in their pool have been expended. Different actions consume different numbers of points, and the maximal number of points that can be spent is determined by a character's total agility statistic and modifying elements such as chems (which are temporary) and perks (which are permanent). "Melee" (hand-to-hand) weapons typically offer multiple attack types, such as "swing" and "thrust" for knives. Unarmed attacks offer many attack types, including "punch" and "kick". Players may equip at most two weapons, and the player can switch between them at the click of a button. The "perception" attribute determines characters' "sequence" number, which then determines the order of turns in combat; characters with a higher statistic in this attribute are placed at an earlier position in the sequence of turns, and subsequently get new turns earlier. Perception also determines the maximal range of ranged weapons and the chance to hit with them.
A diverse selection of recruitable non-player characters (NPCs) can be found to aid the player character in the post-apocalyptic wasteland. Examples include Ian, an experienced traveler and gunman, who can use pistols and submachine guns; and Dogmeat, a dog the player may recruit in Junktown by either wearing a leather jacket or feeding the dog an iguana-on-a-stick. Unlike Fallout 2, there is no limit to the number of NPCs that the player may recruit, and NPCs' statistics and armor in Fallout remain unchanged through the entire game; only their weapons may be upgraded.
An example of dialogue between characters in Fallout
The protagonist is governed by the system called S.P.E.C.I.A.L (an acronym for "Strength, Perception, Endurance, Charisma, Intelligence, Agility and Luck"), designed specifically for Fallout and used in the other games in the series. The player begins Fallout by selecting one of three characters to play as the protagonist, or alternatively, they can create one with custom attributes using the system. Character development is divided into four categories: attributes, skills, traits, and perks. These have been copied or otherwise adapted in some form or another through the ensuing iterations of the series.
Strength, perception, endurance, charisma, intelligence, agility and luck are the seven basic attributes of every character in the game. The SPECIAL stats continually add bonuses to skills. This is done automatically, i.e. if the SPECIAL stats change, the bonuses are instantly adjusted. Some "perks" and coded events within the game require that the player has a certain level of particular SPECIAL stat before accessing it.
There are 18 different skills in the game, ranging in value from 0 to 200%. The starting values for Level 1 skills are determined by the player's seven basic attributes, and most initially fall within the range of 0 to 50%. Every time the player gains a level, skill points are awarded, which can be used to improve the character's skills. The player may choose to tag three skills that will improve at twice the normal rate and receive a bonus at the start. Skills are divided into three categories: combat, active and passive. Books, although scarce in the early game, can be found throughout the game world and permanently improve a specific skill when read. However, after a skill reaches a certain level, books no longer have an impact. Some NPCs can also improve skills by training. Some skills are also improved by having certain items equipped. For instance, a lockpick improves lock-picking skills. Stimulants can also temporarily boost a player's skills, however, they often have adverse effects such as addiction and withdrawal.
Traits are special character qualities that can have significant effects on gameplay. At character creation, the player may choose up to two traits. Traits typically carry benefits coupled with detrimental effects. For example, the trait "small frame" improves agility by one point, but negatively affects maximal carrying capacity. Once a trait is chosen, it is impossible to change, except by using the "mutate" perk, which allows a player to change one trait, one time.
Perks are a special element of the level-up system. Every three levels (or every four if the player chooses the "skilled" trait), the player is presented with a list of perks and can choose one to improve their character. Perks grant special effects, most of which are not obtainable through the normal level-up system. These include letting the player perform more actions per round or being able to heal wounds faster. Unlike traits, perks are purely beneficial; they are offset only by the infrequency with which they are acquired.
The game also tracks the moral quality of the player character's actions using a statistic called "karma", as well as a series of reputations. Karma points are awarded for doing good deeds and are subtracted for doing evil deeds. The player character may receive one of a number of "reputations", which act like perks, for meeting a certain threshold of such actions or for engaging in an action that is seen as singularly and morally reprehensible. The effect of both karma and reputations is subtle, altering the reactions of some NPCs in game altering ways (for example, the player may complete a quest, but not receive the greatest possible reward due to their low karma).