The U.S.C.S.S. Nostromo is an M class starship owned by Weyland-Yutani. It was refitted to be a commercial towing vessel in 2116. The Nostromo has a mass of 63,000 metric tons. Its frame is based on a modified Lock-mart CM-88B Bison Transporter. The ship has three pressurized decks and four main cargo holds. The spare volume is taken up by the fuel tank for the fusion reactor and the reaction mass for the thrust engines. An off-axis hooded frame mounts the docking latches for the towed cargo. The Nostromo is strong enough to withstand atmospheric re-entries with micro-meteorite and particulate shielding, and for surface landings, it's supported by three main landing shocks. Its in-flight systems are controlled by Mother, a central computer processor, which is able to process commands given by the crew onboard. Dallas is the captain in charge of the ship when it lands on LV-426 in 2122. The vessel gets damaged during the landing, and an Alien is brought back onboard. Eventually, Ripley, the ship's warrant officer, sets the vessel for self-destruct and escapes in the ship's escape shuttle, the Narcissus. The Nostromo is worth over 42 million in adjusted dollars, and that estimate doesn't include its payload. The Nostromo's name comes from the title of a Joseph Conrad novel about a vessel carrying ore out of a troubled South American country.

Found on an unsurveyed planet later designated as LV-426, the Derelict Ship is the source of an acoustical transmission picked up by the Nostromo. Originally thought to be an S.O.S., the signal is actually a warning. A three-man rescue team enters the massive U-shaped Derelict through a circular opening on its side. Inside the ship, they encounter a giant fossilized creature unlike any ever seen before. Commonly called the Space Jockey, this is believed to be the pilot of the spacecraft. It appears to have died when an Alien burst out of its chest. In that same room, there is a hole in the floor that leads to a huge chamber below. Kane gets lowered down into this, finding thousands of Eggs. They have a thin blue mist covering them, which reacts when broken. This is thought to be a form of containment. When Kane disturbs one of the Eggs, a Facehugger leaps out, breaking through his spacesuit and attaching itself to his head. Dallas and Lambert drag him back to the Nostromo. Not long after, they take off, leaving the preserved Alien ship on the planet. The Derelict is one of the great mysteries of the series. One theory about the Space Jockey race is that they created the Alien as a biological weapon. Xenomorphs were stored onboard the Derelict as they were sent to another planet in order to conquer it, but something went wrong, and the Aliens escaped. The pilot became host to a Facehugger while the rest of its crew was killed. The original idea behind all the Eggs on the Derelict is that they were the Jockey's crew who were killed and transformed by the Alien.

The Narcissus is a small interstellar shuttle-craft and lifeboat, which was modified from a Lock-mart Star-cub Light Intrasystem Shuttle. Its mass is 48 metric tons. The Narcissus is configured around a single 108 m3 pressure cabin. Ripley leaves the Nostromo in this escape shuttle moments before the Nostromo's explosion. She discovers the Alien had been hiding onboard too, but she blows it out of the spacecraft's airlock. Then the Alien climbs into one of the shuttle's four aft thrusters, but Ripley turns on the vessel's engines, killing the Alien. After this, Ripley and her cat, Jones, go into hypersleep in the shuttle's cryotube. 57 years later the Narcissus is found by a deep salvage team. Its passengers are still alive.