Perks in Fallout are acquired every three levels (four with the Skilled trait), with the first available at level 3 (4). As such, the player can choose seven perks (five with the trait) out of a total of 53. Some perks have multiple ranks, with stacking benefits (all benefits are listed per-level). It is possible to obtain perks that the player's character doesn't qualify for by the use of temporary stat improving chems before the selection menu (i.e. a character with 4 Intelligence can use Mentats to select the Educated perk, which requires 6 Intelligence).
One quirk of Fallout and its sequel is that no effort was made to balance the perks, due to the last-minute replacement of GURPS with SPECIAL. As such, out of the 53 perks only a dozen are implemented in a fashion that gives a functional benefit. Perks like Awareness (detailed combat information) or Bonus Rate of Fire/Bonus HtH Attacks (global reductions of AP costs for attacks) are effectively mandatory for the player due to their impact on gameplay. The remainder of beneficial perks include Action Boy/Girl, Bonus Move, More Criticals/Better Criticals, Quick Pockets, Dodger, and Toughness, i.e. perks that improve combat performance.
The remaining 43 perks are largely useless due to systemic issues present in SPECIAL and general game balance (or lack thereof):
The limited amount of experience points and arbitrary level limit make perks focused on increasing the rate of experience gain (Swift Learner), provide per-level benefits (Lifegiver), or consume a perk slot to alter the trait selection (Mutate!). They also relegate perks like Slayer or Sniper to curiosities, as they are not available without significant grinding. At the same time, each level-up provides enough skill points to eliminate the need to pick Educated, Master Thief, Medic, Mr. Fixit, or Speaker. Unlike later games, these perks do not unlock any additional dialogue options either.
Design of stealth and theft is primitive. Failure to steal causes most, if not the entire map, to become permanently hostile, as does failing to sneak (Ghost, Silent Death, Silent Running, and Pickpocket).
Dialogues have systems that are poorly or even unimplemented. The reaction system is fundamentally broken, making it nearly impossible for a character to react negatively (rendering Cult of Personality, Empathy and Presence useless), while Speech is far more important than Intelligence (Smooth Talker).
Lack of balance in combat marginalizes most combat perks. Bonus HtH Damage and Bonus Ranged Damage offer minimal bonuses, Earlier Sequence is meaningless due to the way turn-based combat is implemented in the game, Rad Resistance and Snakeater increase resistance to marginal threats, Night Vision and Sharpshooter have a limited impact due to the underlying chance to hit calculation that prioritizes weapon skills, while Animal Friend does not affect genuine threats like deathclaws. Heave Ho! does not have any effect unless the player character's strength is less than 4 (and affects weapons of marginal usability). Friendly Foe is a perk that should have been a default part of the interface and is implemented as such in Fallout 2.
The limited variety of world map encounters and the reliance of special encounters on raw Luck renders Explorer, Mysterious Stranger, Pathfinder, Ranger, Scout, Scrounger, and Survivalist meaningless.
The remainder of perks is affected by general balance. Strong Back is rendered meaningless by the infinite capacity of party members like Ian, while Fortune Finder and Master Trader have little impact due to structural flaws of the bartering system (where items the player sells are always sold at full value). The ready availability of a psychic nullifier eliminated Mental Block, while the presence of stimpaks does the same for Faster Healing, and Healer. The lack of permanence for drug addiction claims Flower Child as well.