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The writing partnership between Dan O'Bannon and Ronald Shusett came about when Shusett approached O'Bannon about helping him adapt a Philip K. Dick story to which he had acquired the rights. That was "We Can Remember It for You Wholesale," which later became Total Recall (1990). O'Bannon then said that he had an idea that he was stuck on, about an alien aboard a spaceship, and that he needed some assistance. Shusett agreed to help out, and they tackled the alien movie first, as they felt it would have been the cheaper of the two to make.
The blue laser lights that were used in the alien ship's egg chamber were borrowed from The Who. The band was testing out the lasers for their stage show in the soundstage next door.
The chestbursting scene was NOT filmed in one take (despite the myth). The scene was filmed twice: on the first take, the chestburster did not make it through Kane's shirt, so the crew needed to reset and shoot it again. The failed attempt is visible in the finished film since Ridley thought it made it look like the creature was struggling to push its way out, and made the scene more violent. (See The Beast Within documentary where this is discussed).
Shredded condoms were used to create tendons of the beast's ferocious jaws.
According to Yaphet Kotto, Sir Ridley Scott told him to annoy Sigourney Weaver off-camera, so that there would be genuine tension between their characters. Kotto regretted this, because he really liked Weaver.
To get Jones the cat to react fearfully to the descending Alien, a German Shepherd was placed in front of him with a screen between the two, so the cat wouldn't see it at first. The screen was then suddenly removed to make Jones stop advancing and start hissing.