The film is divided into three parts. 

Part I: The Dawn of Man The film opens in the late Pliocene, 3 million years ago, as a tribe of pre-human apes struggles for survival in a harsh wildland. They forage for wild plants, run from predators, and are forced to retreat from their watering hole by an opposing tribe. Returning to their shelter, the apes stumble upon a tall, black monolith, which they cautiously touch. The apes then begin using nearby animal bones as weapons, allowing them to hunt for meat and seek violent retribution against their enemy tribe. Celebrating his victory, an ape stands on his hind legs and tosses his bone weapon into the air. With the weapon soaring into the sky, the film abruptly cuts to a satellite orbiting Earth. The year is now 2001, and scientist Dr. Heywood Floyd (William Sylvester) is traveling via space shuttle to a Moon base that has unearthed a monolith on the lunar surface. As Heywood and his research group gather for a photo in front of the monolith, a shrill, piercing tone fills their radio transmission, and the film cuts to black.  

Part II: Jupiter Mission: Eighteen Months Later A team of American scientists aboard the spaceship Discovery One has been sent on a mission to explore Jupiter. The team consists of the pilots, Dr. Dave Bowman (Keir Dullea) and Dr. Frank Poole (Gary Lockwood), three scientists in cryo-stasis, and the Heuristically programmed ALgorithmic supercomputer, HAL 9000 (Douglas Rain). HAL runs all onboard operations with mathematical precision but confides in Dave that he is anxious about their mission. HAL predicts that a communication device on the ship’s exterior will fail if it is not urgently repaired. Dave pilots an extravehicular activity (EVA) pod and retrieves the device but finds nothing wrong. HAL maintains that his prediction is correct and suggests the device should be allowed to fail to identify the problem. Mission Control advises that their supercomputer ascertained that HAL has made an error, which HAL denies, stating the only error is human error.  

Dave and Frank shut themselves in an EVA pod, outside the range of HAL’s microphones, and decide to shut down HAL if his prediction proves to be untrue. However, HAL’s camera records this surreptitious conversation and he reads the pilots' lips. Frank leaves the Discovery in an EVA pod to reinstall the communication device. HAL hijacks the EVA pod and uses it to remove Frank’s air supply, killing him. Dave sees Frank’s body floating off into space and asks HAL what happened, to which HAL replies he doesn’t know. Dave quickly jumps into another EVA pod, forgetting his helmet. While Dave retrieves Frank’s body outside the Discovery, HAL turns off the life support for the scientists in cryo-hibernation, killing them. HAL then locks the door to the EVA bay, denying Dave entry back onto the Discovery. HAL tells Dave that the plan to deactivate him will compromise the mission.  

Dave ejects himself from his EVA pod and manually opens the emergency airlock, miraculously surviving without his helmet. Back aboard the Discovery, Dave disconnects HAL’s circuits, while HAL pleads with Dave to stop. As he ceases to function, HAL reveals that his “mind is going” and that he is “afraid.” Dave is shaken by “killing” HAL. With HAL offline, a recording from Heywood automatically begins playing, revealing that the true purpose of the Jupiter mission is to investigate a signal that the lunar monolith sent to Jupiter.  

Part III: Jupiter and Beyond the Infinite Dave, now the lone surviving member of Discovery One, arrives in Jupiter’s orbit. He encounters a massive monolith orbiting the planet. As Dave approaches the monolith in an EVA pod, he enters a tunnel of intense flashing colors. He awakens in a neoclassical apartment. He then experiences a strange aging phenomenon, which ends with him as an old man lying in bed. He sees the monolith at the foot of the bed and reaches for it. The film ends with Dave transformed into a fetus suspended in a ball of light, orbiting Earth.