The original screenplay focused mainly on Rachel, but director Peter Weir asked screenwriters William Kelley and Earl W. Wallace to rewrite it to focus on the comparison of pacifism and violence as seen through the eyes of John Book.
In the scene where Book sits down to early morning breakfast with the Lapps, he quips, "Honey, that's great coffee," shocking Rachel by seeming to refer to her as "honey". He then explains that this was a joke, from some commercial. Among the personal quotes for Harrison Ford appears the basis for this line when the actor was commenting on the early days of his career: "I started by chasing a Folger's commercial. But I just somehow couldn't manage to say, 'Honey, that's a great cup of coffee'".
This film was released in early 1985. It was the number two film at the box office behind the enormous hit Beverly Hills Cop. Even though this film made money, a Paramount executive said that if they had known "Cop" was going to be such a big hit, they would not have released this film so soon after it.
An advertiser wanted to capture the look of this film for a TV commercial for his product. When he interviewed directors of photography, he told them he wanted the look of this film. One of the people interviewed was John Seale, the director of photography for this film. Ironically, Seale did not get the job.
The "evening serenade" scene in the barn, in which Book and Rachel dance, was actually filmed during the day in the heat of the summer. The barn was blacked out and sealed, and that's why both Harrison Ford and Kelly McGillis perspire so much in that scene. The kerosene lantern they had added even more heat.
The song for the "serenade" scene, "Wonderful World" by Sam Cooke, was selected by Harrison Ford himself. Director Peter Weir said that since Ford had to sing and dance to it, he should be able to choose which song he wanted to use for that scene. However the version of the song heard in the film is not Sam Cooke's original, but performed by Cooke sound-alike Greg Chapman.
As realistic as the actors playing background roles as Amish people are, no actual Amish were in the film because they do not (as is correctly stated in the film itself) like to have their pictures taken. They were intensely interested in the filming, though, and many Amish people were often out of camera range politely watching the filming.
In preparation for her role, Kelly McGillis lived with an actual Amish widow and her seven children for a period of time before filming began to get the speech cadence down and to observe the daily life of an Amish widowed mother.
The story for Witness was originally a plot outline for the TV series Gun Law. The writers William Kelley and Earl W. Wallace had both been writers on Gunsmoke and their original story had Marshall Dillon traveling to an Amish farm looking for a witness to a murder.
Although he once again plays a heroic man with a gun, Witness was the first starring role that broke Harrison Ford away from the science fiction and fantasy genres that made him famous and gave him his first and only Academy Award nomination for Best Actor.
When producer Edward S. Feldman, who had a first-look development deal with 20th Century Fox, first received the script, it ran to 182 pages which is the equivalent of three hours screentime. Feldman was really enthusiastic about the screenplay even though he felt that there was too much concentration on the Amish and their traditions. He offered writers William Kelley and Earl W. Wallace $25,000 for a one-year option and a rewrite, plus an additional $250,000 if the film ever got made. Kelley and Wallace submitted their revised screenplay within six weeks, and Feldman promptly submitted it to Fox and its studio head, Joe Wizan. Who immediately rejected the script with the statement that Fox didn't do "rural movies".
Producer Edward S. Feldman's first choice for director was Peter Weir from the very start. Weir, however, turned it down because he was involved in pre-production on The Mosquito Coast. Feldman then went to John Badham who dismissed it as "just another cop movie". After being turned down by various other directors, Feldman was delighted when Weir suddenly became available again as his production of The Mosquito Coast had been delayed due to finance difficulties. Weir would ultimately make The Mosquito Coast in 1986 with Harrison Ford starring.
When shooting the murder in the men's room scene, Peter Weir claimed it was the most violent scene he'd ever filmed. Even today, he still thinks it was perhaps too violent. But he wanted to have an outrage over the violence that occurred before the eyes of an innocent Amish boy.
The studios weren't keen on the production initially because they thought it was too rural. Even when Harrison Ford agreed to star in it, despite the signing of a major name, they still weren't interested in it.
The Amish were critical of the film. They felt their portrayal was not accurate. The National Committee For Amish Religious Freedom called for a boycott on the movie, citing fears that these communities were "overrun by tourists" because of the popularity of the film. They worried that "the crowding, souvenir-hunting, photography and trespassing on Amish properties would increase as a result." When the film was finished, the governor of Pennsylvania promised not to promote the Amish film communities as future film sites.
The statue that Samuel examines in the train station is a real monument in Philadelphia's 30th Street Station. It is a memorial to the men and women of the Pennsylvania Railroad who died during World War Two. Its official title is "Angel of the Resurrection," and it is a depiction of the archangel Michael lifting a deceased soldier from the battlefield. Walker Hancock was the sculptor; it was dedicated in August 1952 and, as of June 2012, still stands on the east side of the station's main concourse.