Fallout 3 gameplay
 Character creation and advancement
The player character has primary stats, skills and perks - all numerical values which determine actions' chances of success according to mathematical formulas, as well as derived statistics such as hit points. Beginning stats are chosen during a series of tutorial quests and may be changed just before exiting Vault 101.
Experience points are awarded for successful completion of actions. Acquiring enough experience points causes the player character to level up, upon which skill points are distributed by the player and an additional perk chosen.
The game features both first-person and over-the-shoulder third-person perspective, toggleable at the player's choice.
The Vault-Tec Assisted Targeting System, or V.A.T.S., is an active pause combat system. While using V.A.T.S., the otherwise real-time combat is paused. V.A.T.S. will also allow the gory deaths in the game to be shown in slow motion and close-up detail. Attacks in V.A.T.S. cost action points, and the player can target specific body areas for attacks to inflict specific injuries.
Outside of V.A.T.S., combat takes place in real time.
 Weapons and armor
The player will have a maximum party of three, consisting of the player character, Dogmeat and one of the available humanoid followers. Followers become available based on the player character's karma.
When in dialogue with an non-player character, the player character chooses responses from a list. Dialogue choices which are dependent on a skill or stat check will display a chance of success next to the text. Dialogue choices can determine quest rewards, karma level, non-player character reaction level, as well as other effects.
The player character's actions, including conversation and combat choices, affects the player's status in the game world; a player who chooses good actions will be received more positively by non-player characters, and a player that chooses bad actions will have the opposite reaction.
Whichever faction or group that is harmed by a crime will be fully aware of the player character's action. Other factions that were not affected by the crime will not be aware of it, and since a town is usually its own faction, news of a crime committed in one town will not spread to another. Factions can range in size and boundaries, however, and may not be restricted to a single area.
Some perks become available based on karma level.
Lockpicking in Fallout 3 requires two things: a bobby pin, used to pick the lock, and a sufficient ranking in the Lockpick skill to be able to pick the lock. The bobby pin is moved into position by the player, and then the lock turned with a screwdriver. If the bobby pin is in the right location, it will open the lock. If the bobby pin is not in the right position, the bobby pin may break. The player also has the option to try to force the lock, but if the attempt fails, the lock will be broken and can only be opened with a key, or reset with the Infiltrator perk.
Hacking requires that the character be at the sufficient Science level to attempt the hack. The minigame is a logic puzzle, similar to the board game Mastermind, with the player having to guess the passcode out of a pool of given words. Upon choosing a codeword out of the list, the computer will either login (if the word is correct), or tell the player how many letters are correct. Based on this information, the player may guess another word. The player has four attempts to find the correct word: if the fourth guess is incorrect, the computer will lock the player out of the system until the player receives the correct password, or the system is reset upon obtaining the Computer Whiz perk.
 Changes from previous Fallout games
- While Fallout and Fallout 2 featured turn-based combat and top-down isometric view in a 2-D engine, Fallout 3 features real-time combat and first or third person view in a 3-D engine.
- In the SPECIAL character system, the number of skills has been reduced from 18 to 13, and perks are selected every level instead of every 3 to 4 levels. Traits have been removed and retooled into new perks.