The game takes place in an underwater city named Rapture. Surviving a plane crash at the beginning of the game you find your way to this lost city, a decrepit and crumbling shadow of its former self. The ocean is reclaiming the space, and the inhabitants have turned into bloodthirsty mutants. During the course of the game you uncover how Rapture fell from its grace of a 1940s Utopian dream to the current nightmare. Minimal use of cutscenes are used as information is spread around the environment itself in newspapers, posters, and radio broadcasts.

At its core the game is a first person shooter, meaning you run around the environment in the first person perspective shooting and killing your enemies. Irrational is trying to mix up the formula by giving players many options to work with. There are eight weapons available that can be customized with various options, alongside the 60 abilities that are found in the game. Abilities, or Plasmids as they're known in the world, let you perform superhuman acts such as launching fire, electricity, or confusing your enemies.

BioShock differs from other games in that the enemies are not out to specifically get you. Irrational games states that each character in the world of Rapture has their own "brain" and motivations, usually revolving around the harvesting of ADAM which is the oil/money/water of the world. Since ADAM is a very limited resource that results in you battling the other characters, but also results in the characters battling each other.

Both a PC version and Xbox 360 version are set for simultaneous release. Both versions of the game have received design and optimization to ensure the interface suits mouse and keyboard, and a controller respectively.