In August 2013, HBO announced plans for a TV adaptation based on the original film. The series has enjoyed two highly succesful seasons with a third pending release in 2019.
In the near future, there is a high-tech, highly realistic adult amusement park called Delos that features three themed "worlds" — Westworld (the American 'Wild West' from the 1880s), Medieval World (medieval Europe), and Roman World (pre-Christian Rome). The resort's three "worlds" are populated with lifelike androids that are practically indistinguishable from human beings, each programmed in character for their assigned historical environment. People pay to indulge in adventures in each of the worlds where they interact with the android population. Guests are encouraged to do anything they feel like, including killing any of the androids or having sexual intercourse with the gynoids (feminine robots). The film begins with a TV commercial where a Delos employee is interviewing people at the airport who just returned from Delos and are pleased with their stay, and the employee announcing "Boy, have we got a vacation for you!"
Peter Martin is a first time visitor. He and a friend, John Blane, a return visitor, are taken by hovercraft to Delos' resort in the middle of the desert. The hovercraft disembarks at an underground processing facility. Guests are segregated by color-coding, through yellow (for Roman World), red (for Medieval World) or blue (for Westworld). The guests are attired in clothing appropriate for their chosen period and sent down a tunnel which surfaces in the respective "world". Much of the film is shown with Peter and John in Westworld, although it intersperses with some of the other parts of Delos.
In Westworld, Peter sees that Delos is strict about historical accuracy, right down to the artifacts having been made in the actual years. John says they can use their guns to kill androids, but Peter expresses concern about who is who, considering the androids look identical to guests (with exception of small indentations on the hands). John challenges Peter to shoot him, but when Peter does so, his pistol fails to discharge. John explains that the pistols have heat-sensitive trackers. Androids have a low body temperature, but the pistols do not fire if they detect a certain heat range, in which case they will not activate near the high body temperatures humans are known for. Peter remarks that Delos thought of everything.
The technicians running Delos notice problems are beginning to spread among the androids, but the park managers dismiss the incidents, maintaining confidence in the safety of the resort. The incidents escalate, however. A robot gunslinger which Peter shot down on his first day tracks Peter down and attacks him and John in their hotel. John is later bitten by a robotic snake in Westworld, and a guest in Medieval World is slapped by a robot serving girl after making advances on her. The management agrees to halt incoming guest traffic until the problems are corrected.
Without warning, however, chaos erupts throughout the resort the next morning. A scripted duel between the Medieval World guest and a Black Knight results in the guest being run through and killed. In Roman World, the robots turn en masse on their guests and butcher them. In Westworld, the robot gunslinger challenges Peter and John yet again, and when John accepts, the Gunslinger disables the sensor on his pistol and shoots John down.
In a panic, the staff attempts to shut down power and the androids, but the robots reveal they now have their own power cores and continue to slaughter the guests and outside staff. They also seal the control center and shut down the air supply, suffocating the technicians.
In Westworld, the Gunslinger, now using infared sight and enhanced hearing, forces Peter on a sadistic cat-and-mouse chase through all three parks. Somehow Peter finds an entrance to the maintanance tunnels and arrives at a repair facility for the robots. Acting on advice from one of the last surviving staff members, Peter turns the tables on the Gunslinger. He hides among a group of deactivated robots, and when the Gunslinger gets close, he splashes it in the face with a jar of hydrochloric acid. Peter then lures it into the castle at Medieval world, where he uses heat from wall torches to mask his infrared signature. He manages to set the Gunslinger on fire with a torch and drops it from a staircase into the dungeon, where it sparks and shuts down.
Noticing a young girl chained to the wall, Peter immediately frees her and attempts to give her water, only for her to spark and fail, too - she is a new robot completely indistinguishable from humans. Now the only survivor of the disaster, Peter can only sit in shock as the slogan of the prologue reverbates through his head: "Boy have we got a vacation for you!"
- Yul Brynner as The Gunslinger
- Richard Benjamin as Peter Martin
- James Brolin as John Blane
- Norman Bartold as the Medieval Knight
- Alan Oppenheimer as the Chief Supervisor
- Victoria Shaw as the Medieval Queen
- Dick Van Patten as the Banker
- Linda Scott as Arlette, the French prostitute
- Steve Franken as the Delos Technician shot dead by the Gunslinger
- Michael Mikler as the Black Knight
- Terry Wilson as the Sheriff
- Majel Barrett as Miss Carrie, madame of the Westworld bordello
- Anne Randall as Daphne, the serving-maid who refuses the Medieval Knight's advances
- Nora Marlowe as the Hostess
- Robert J. Hogan as the Delos Guests' Interviewer (uncredited)
The musical score for the film was composed by Fred Karlin. It features a blend of traditional Western film score influences and period music with creative uses of electronic and experimental instrumental music. Homages to elements of Karlin's soundtrack later appeared in the HBO series soundtrack as well.
- Westworld is the first feature film to use digital image processing to pixellate photography to simulate an android point of view.
- Majel Barrett, who plays the madam, is best known as portraying Nurse Chapel and the voice of the computer in Star Trek (Original Series and Next Generation) and for a recurring role in Star Trek: The Next Generation (Deanna Troi's mother, Lwoxana Troi). Barrett was the wife of Star Trek creator Gene Roddenberry.
- Westworld describes the concept of a computer virus extremely early in the development of networked computers, when computer viruses were almost unheard of.
- Westworld is the first time the concept of "intelligent machines (computers) creating other intelligent machines (robots) without human involvement had been described.
- According to the original filming script, the Delos Resort Complex is located inside a climate controlled dome 500 miles from the edge of the Sahara Desert.
- Guests paid $1000 per day to stay at the Delos Resort in the 1973 film. The per day cost to visit the park (HBO series) was quoted by Logan at $40,000.
- Guests were transported to the resort via hovercraft.
- The name of the park was repeatedly identified during the movie as "Western World", while the film was titled "Westworld". The name of the park and show's title remain consistent on the HBO series.
- The system of tunnels running beneath the park complex and the computer control room was inspired by the "utilidore" system and the DACS (digital audio control system) room beneath the Magic Kingdom Park at Walt Disney World in Florida. DACS is/was located beneath Fantasyland. The Magic Kingdom opened in 1971, two years prior to Westworld.
- The tagline, "Where nothing can possibly go worng" (sic) appeared on promotional materials (including the movie poster on the cover of the "shooting" film script now available on Amazon).