This is an action-adventure game in which players assume the role of Chell, a human who is trapped in a scientific testing facility. From a first-person perspective, players solve numerous physical puzzles as they navigate through post-apocalyptic environments. Players use a "portal gun" to open transportation gateways. Throughout the game, players must avoid hazards such as stationary gun turrets, toxic substances, poisonous gas, and giant pistons; some sequences are accompanied by realistic gunfire. Robot droids can also be destroyed; for example, in one boss battle, players must defeat a robot by throwing small bombs. The words "damn" and "hell" can be heard in the dialogue.