It was originally released in a bundle, The Orange Box, for Windows, Xbox 360 and PlayStation 3, and has been since ported to other systems, including Mac OS X, Linux, Android (via Nvidia Shield), and Nintendo Switch.

GLaDOS, voiced by Ellen McLain in the English-language version, received acclaim for her unique characterization, and the end credits song "Still Alive", written by Jonathan Coulton for the game, was praised for its original composition and humor.

Excluding Steam download sales, over four million copies of the game have been sold since its release, spawning official merchandise from Valve including a model portal gun and plush Companion Cubes, as well as fan recreations of the cake.

Particle fields, known as "Emancipation Grills", occasionally called "Fizzlers" in the developer commentary, exist at the end of all and within some test chambers; when passed through, they will deactivate (fizzle) any active portals and disintegrate any object carried through.

[6] Although Chell is equipped with mechanized heel springs to prevent damage from falling,[4] she can be killed by various other hazards in the test chambers, such as turrets, bouncing balls of energy, and toxic liquid.

[9][10] The game features two characters: the player-controlled silent protagonist named Chell, and GLaDOS (Genetic Lifeform and Disk Operating System), a computer artificial intelligence that monitors and directs the player.

However, after becoming mentally unstable from "moon rock poisoning" in 1978, Johnson created a three-tier research and development plan to make his organization successful.

However, when the investigative committee heard of the success of the third tier—a person-sized, ad hoc quantum tunnel through physical space, with a possible application as a shower curtain—it recessed permanently and gave Aperture Science an open-ended contract to continue its research.

The development of GLaDOS, an artificially intelligent research assistant and disk-operating system, began in 1986 in response to Black Mesa's work on similar portal technology.

[18] As Chell nears completion, GLaDOS's motives and behavior turn more sinister, suggesting insincerity and callous disregard for the safety and well-being of test subjects.

[b] The final scene, viewed within the bowels of the facility, shows a candlelit Black Forest cake,[23] and a Weighted Companion Cube, surrounded by shelves containing dozens of inactive personality cores.

[28] Newell said he was impressed with the team as "they had actually carried the concept through", already having included the interaction between portals and physics, completing most of the work that Valve would have had to commit on their own.

[35] The concept of a computer AI guiding the player through experimental facilities to test the portal gun was arrived at early in the writing process.

"[36] Wolpaw described the idea of using cake as the reward came about as "at the beginning of the Portal development process, we sat down as a group to decide what philosopher or school of philosophy our game would be based on.

"[36] The Weighted Companion Cube inspiration was from project lead Kim Swift with additional input from Wolpaw from reading some "declassified government interrogation thing" whereby "isolation leads subjects to begin to attach to inanimate objects";[31][36] Swift commented, "We had a long level called Box Marathon; we wanted players to bring this box with them from the beginning to the end.

[42] Most of the soundtrack is non-lyrical ambient music composed by Kelly Bailey and Mike Morasky, somewhat dark and mysterious to match the mood of the environments.

The closing credits song, "Still Alive", was written by Jonathan Coulton and sung by Ellen McLain (a classically trained operatic soprano) as the GLaDOS character.

[47] The soundtrack was released in a four-disc retail bundle, Portal 2: Songs To Test By (Collector's Edition), on October 30, 2012, featuring music from both games.

[52] The Windows version of the game is also available for download separately through Valve's content delivery system, Steam,[1] and was released as a standalone retail product on April 9, 2008.

[24] In January 2008, Valve released a special demo version titled Portal: The First Slice, free for any Steam user using Nvidia graphics hardware as part of a collaboration between the two companies.

[58] A similar promotion was held in September 2011, near the start of a traditional school year, encouraging the use of the game as an educational tool for science and mathematics.

[59][60] Valve wrote that they felt that Portal "makes physics, math, logic, spatial reasoning, probability, and problem-solving interesting, cool, and fun", a necessary feature to draw children into learning.

[73][74] Nvidia announced Portal With RTX, a remaster intended to show off the functionality of the company's GeForce 40 series graphics cards with real-time path tracing,[75] for release as a free DLC, initially planned for November 2022.

[76] Portal received critical acclaim, often earning more praise than either Half-Life 2: Episode Two or Team Fortress 2, two titles also included in The Orange Box.

[80] Eurogamer cited that "the way the game progresses from being a simple set of perfunctory tasks to a full-on part of the Half-Life story is absolute genius",[81] while GameSpy noted, "What Portal lacks in length, it more than makes up for in exhilaration.

[89][90][91] Jeep Barnett, a programmer for Portal, noted that players have told Valve that they had found it more emotional to incinerate the Weighted Companion Cube than to harm one of the "Little Sisters" from BioShock.

[95] Writing for GameSetWatch in 2009, columnist Daniel Johnson pointed out similarities between Portal and Erving Goffman's essay on dramaturgy, The Presentation of Self in Everyday Life, which equates one's persona to the front and backstage areas of a theater.

[134] Other products available through the Valve store include T-shirts and Aperture Science coffee mugs and parking stickers, and merchandise relating to the phrase "the cake is a lie", which has become an internet meme.

The original game left her in a deserted parking lot after destroying GLaDOS, but the update involved Chell being dragged back into the facility by a "Party Escort Bot".

[145] Another mod, Portal: Prelude, is an unofficial prequel developed by an independent team of three that focuses on the pre-GLaDOS era of Aperture Science, and contains nineteen additional "crafty and challenging" test chambers.