Andrew Taylor Weir (born June 16, 1972) is an American novelist and former computer programmer. His 2011 novel The Martian was adapted into the 2015 film of the same name directed by Ridley Scott. He received the John W. Campbell Award for Best New Writer in 2016.

Weir began writing science fiction in his twenties and published work on his website for years. He also authored a humor web comic called Casey and Andy featuring fictionalized "mad scientist" versions of himself and his friends (such as writer Jennifer Brozek) from 2001 to 2008; he also briefly worked on another comic called Cheshire Crossing bridging Alice in Wonderland, Peter Pan, The Wizard of Oz and Mary Poppins. The attention these gained him has been attributed as later helping launch his writing career, following the failure to publish his first novel attempt called Theft of Pride. His first work to gain significant attention was "The Egg", a short story that has been adapted into a number of YouTube videos, a one-act play, and is the overarching concept of Everybody, the third album by American rapper Logic.

In 2017 CBS picked up a pilot written by Weir titled Mission Control, following a group of young NASA astronauts and scientists. In May of the same year, Weir collaborated with webcomic artist Sarah Andersen to remake Cheshire Crossing for Tapas, before publishing it as a stand-alone graphic novel in July 2019. In November 2019, a film adaptation was announced from Amblin Partners and Walt Disney Pictures, to be produced by Michael De Luca and written by Erin Cressida Wilson.

In May 2021, Weir's third novel, Project Hail Mary, was released. The plot revolves around an astronaut, Ryland Grace, who wakes up from a coma on a strange spacecraft and is afflicted with amnesia. Ryan Gosling is slated to produce and star in a film adaption.