A Scanner Darkly is a 2006 film by Richard Linklater starring Keanu Reeves, Winona Ryder, Woody Harrelson, Robert Downey, Jr., and Rory Cochrane. It is based on the Philip K. Dick novel of the same name. Steven Soderbergh and George Clooney are among the film's executive producers. The film was written and directed by Richard Linklater in Austin, Texas. It was released on July 7, 2006 in theaters within limited cities including New York City, Los Angeles, San Francisco, Seattle, Boston and Minneapolis. It was distributed in wide release on July 28, 2006. Extensive on-set footage of the filming of A Scanner Darkly was featured in a UK documentary about Richard Linklater directed by Irshad Ashraf and broadcast on Channel 4 in December 2004. The movie was screened at the 2006 Cannes Film Festival and the 2006 Seattle International Film Festival, and the world premiere took place at Brandeis University in Waltham, Massachusetts on April 30, 2006.

In the near future (seven years from now), America has lost the war on drugs.

The main character (Reeves) is both Bob Arctor, part of a household of drug-users, and Fred, an undercover police agent assigned to spy on them. Arctor/Fred shields his true identity both from those in the drug subculture and, ironically, from the police themselves through use of "scramble suits" that he and others must wear while at the police station. The requirement that narcotics agents remain anonymous, to avoid collusion and other forms of corruption, becomes a critical plot point. While supposedly only posing as a drug user, Arctor becomes addicted to Substance D (often known simply as Death), a powerful psychoactive drug. An ongoing conflict is Arctor's love for Donna Hawthorne (Ryder), a fellow user of Substance D and cocaine. Arctor's persistent use of Substance D, which causes the two hemispheres of the brain to function independently, leaves him unable to distinguish between his roles as a drug user and a policeman. Through a series of drug and psychological tests, Arctor's superiors at work discover that his addiction has made him incapable of performing his job as a narcotics agent. Donna is then revealed to the audience as Arctor's superior officer (previously known simply as "Hank" because of her scramble suit). After revealing to Arctor that she knows his identity, Donna takes Arctor to "New Path", a rehabilitation clinic, just as Arctor begins to experience the symptoms of Substance D withdrawal. Donna, who had been a narcotics agent all along, was part of a police operation to infiltrate New Path and determine its funding source. Unknowingly, Arctor had been selected to carry out the sting.

As part of the rehab program, Arctor is renamed "Bruce" and forced to participate in psychological reconditioning. The story ends with Arctor working at a New Path farming commune, where he is suffering from a serious neurocognitive deficit after withdrawing from SD. Arctor realizes that the farm's actual crop is the flower used to make Substance D; as the film ends, he hides one of the flowers on his person, intending to give it to Donna later as evidence.

The end credits list people who have suffered serious permanent physical or mental damage (brain damage, psychosis, pancreatic trauma, etc.) or death as a result of massive drug use. The names are found in the afterword ("Author's Note") of the novel. The note that Dick wrote to accompany this list is also faithfully reproduced in these end credits, in which he mourns their deaths and destruction. Dick includes his own name on the list, as a victim of pancreatic failure.

Linklater himself adds another name to the end credits and dedicates the film to the memory of Louis Mackey. Mackey was an influential philosophy professor at the University of Texas, Austin, who had appeared in two of Linklater's previous films and who died in 2004.

Though a faithful adaptation, the film version of A Scanner Darkly differs in some ways from the novel:

The novel, published in 1977, takes place in 1994. The film takes place in 2013, assuming the "seven years from now" setting is in relation to the film's 2006 release date.
The novel's characters of Jerry Fabin and Charles Freck are combined into Freck.
In the film, "Hank" is revealed to be Donna. In the novel, Hank's identity is never revealed, only the fact that Donna is a narcotics agent.
All references to the "cephalochromoscope" (or "cephscope"), a recreational device that displays brain patterns, have been removed.
Despite taking place in 1994, the dialogue in the novel is rife with the 1970s hippie slang that was prevalent when it was written. None of the hippie slang is featured in the film.
As with all film adaptations of novels, numerous scenes and subplots were not included in the film, such as Arctor visiting a female friend trapped in an abusive relationship and Arctor attempting to admit himself to New Path to track down a drug smuggler he believes to be hiding there.
The Lions Clubs, where Fred/Bob gives a speech early in the novel/film, was changed to the fictional Brown Bear Lodge. Also, McDonald's was changed to the fictional General Burgers.

A Scanner Darkly was filmed digitally using the Panasonic AG-DVX100 and then animated with Rotoshop, a proprietary graphics editing program created by Bob Sabiston. Rotoshop uses an animation technique called interpolated rotoscope, which was previously used in Linklater's film Waking Life. Linklater discussed the ideas and inspiration behind his use of rotoscoping in a UK documentary about him in 2004, linking it to his personal experiences of lucid dreaming. Rotoscoping in traditional cell animation originally involved tracing over film frame-by-frame. This is similar in some respects to the rotoscope style of filmmaker Ralph Bakshi. Rotoscope animation, however, makes use of vector keyframes, and interpolates the in-between frames automatically. Sabiston and his team initially managed this unprecedented animation pipeline, but at the time of his departure, art direction in the studio was still not established and the film's production process was extended well past its initial September 2005 release date target. Each minute of animation required 500 hours of work.

The score (more than an hour's worth is in the film) was provided by Austin, Texas-based composer Graham Reynolds. Linklater approached Reynolds in 2003 after a club performance and suggested Reynolds create the score for A Scanner Darkly. Linklater and Reynolds had worked previously on Live from Shiva's Dance Floor, a 20 minute short featuring Speed Levich.

The composition and recording process took over one and a half years (the unusual time allotment was due to the film's time-consuming animation process) and was done in Reynolds' east Austin home, in his bedroom. This is not a synthesized score; all the instruments except electric guitar and bass were acoustic, though many were transformed through effects. The film also includes clips of four previously released Radiohead songs ("Fog","pulk/pull revolving doors" "Skttrbrain" (Four Tet Remix), "The Amazing Sounds of Orgy") and one new Thom Yorke song, Black Swan.

The album is available from Lakeshore Records (Mr. and Mrs. Smith, Lord of War) and includes the score by Graham Reynolds featuring the Golden Arm Trio. Additionally, the CD includes exclusive remixes of Graham's music by DJ Spooky and Jack Dangers (Meat Beat Manifesto). After finishing the film, Reynolds set to work on remixing the surround sound music into stereo. He then selected 44 minutes out of the film score in order to craft a listening CD while attempting to retain some feel of the arc of the film. Some of the shorter cues were assembled into longer CD tracks.