Once in the filmmaking mindset, and having written teleplays before, Michael Crichton also went for writing screenplays, beginning with Extreme Close-up (1973), also known as Sex Through a Window, and one of his most famous screenplays, Westworld (1973). In 1978 two further screenplays were made into films by himself, with Coma, based on Robin Cook's novel, and The First Great Train Robbery, which is the only one which he wrote, directed and was based on one of his own novels. Later he again directed himself his own screenplays for Looker (1981) and Runaway (1984).
In 1974, Michael Crichton wrote a screenplay that would become the script for the pilot episode of ER in 1994.
Michael Crichton is also listed as co-writer of the screenplay of the adaptations of his novels Jurassic Park and Rising Sun, both released in 1993.
In 1996 he co-wrote the screenplay for Twister with his then wife Anne-Marie Martin, whom he had met on the set of Runaway.
Anne-Marie Martin, on the set of Runaway