Given the extraordinary chemistry between the two leads, it's curious that Humphrey Bogart and Ingrid Bergman never appeared in another movie together, this being their one and only joint venture.
High school teacher Murray Burnett co-authored the play while on summer vacation.
In 2007, the American Film Institute ranked this as the #3 Greatest Movie of All Time.
In the 1980s, this film's script was sent to readers at a number of major studios and production companies under its original title, "Everybody Comes to Rick's". Some readers recognized the script but most did not. Many complained that the script was "not good enough" to make a decent movie. Others gave such complaints as "too dated", "too much dialog" and "not enough sex".
In the famous scene where the "Marseillaise" is sung over the German song "Watch on the Rhine", many of the extras had real tears in their eyes; a large number of them were actual refugees from Nazi persecution in Germany and elsewhere in Europe and were overcome by the emotions the scene brought out.
In the German version, the immortal line "Here's lookin' at you, kid", became, "Ich seh' Dir in die Augen, Kleines" which translates as "I look in your eyes, honey".
In the market scene, as one of the Resistance members is shot, the wall of the building behind him is painted with a picture of Marshal Pétain and a quote attributed to him. In English, the quote reads, "I keep my promises, even those of other people".
In the original script for Casablanca, then titled "Everyone Come to Rick's", Ilsa was not a 'virtuous' woman. She was living with an already married American business man. It was Rick who left her when he found out. And when she and Victor come to Casablanca, she is not married to him, either.
It is never revealed why Rick cannot return to America. Julius J. Epstein later said that "My brother and I tried very hard to come up with a reason why Rick couldn't return to America. But nothing seemed right. We finally decided not to give a reason at all."
It is unclear where the line, "Here's looking at you, kid," originated, but it definitely predated both Casablanca and earlier stage work by Bogart. On March 9, 1932 - 10 years before Casablanca - Eddie Cantor signed his name in cement at Grauman's Chinese Theater and wrote, "Here's looking at you, Sid" (referring to Sid Grauman, owner of the theater). Cantor certainly meant it as a take-off on "Here's looking at you, kid", which evidently was a line in circulation at the time.
It was claimed when the movie was in release that Jack Benny can be seen briefly in it.
It was reportedly Humphrey Bogart's idea to have Rick be a chess player (when we first see Rick he is playing chess against himself), though some say it was writer Howard Koch's idea.
Just before he shot Maj. Strasser (Conrad Veidt), Humphrey Bogart ad-libbed the line, "All right, Major, you asked for it." But Hal B. Wallis pointed out that this made it look as though when Strasser drew his gun first it was self-defense. Veidt was recalled and the scene reshot without the added line, but the original version was used in the trailer for the movie.
Many of the actors who played the Nazis were in fact German Jews who had escaped from Nazi Germany.
No one knew right up until the filming of the last scene whether Ilsa would end up with Rick or Laszlo. During the course of the picture, when Ingrid Bergman asked director Michael Curtiz with which man her character was in love, she was told to "play it in between". Since the ending was not the final scene shot, there are some scenes where she *was* aware of how everything would turn out, and these include the scene in the black market with Rick and the scene in the Blue Parrot where Ferrari offers the Laszlos one exit visa.
Other actresses considered for the part of Ilsa were Edwige Feuillère, Michèle Morgan and Tamara Toumanova. Ingrid Bergman was one of the first choices, but she was under contract to David O. Selznick, who was stalling because he wanted her for For Whom the Bell Tolls. Selznick finally agreed when he learned that the Epstein brothers and Michael Curtiz were working on the film, all of whom he respected and trusted. Warner Bros. also agreed to loan Selznick the services of Olivia de Havilland in return.
Producer Hal B. Wallis considered Hedy Lamarr for the role of Ilsa, but she was then under contract to MGM (which wouldn't release her) and she didn't want to work with an unfinished script anyway. She later portrayed Ilsa in a 1944 radio show based on movie scripts, "Lux Radio Theater". At the time both Ingrid Bergman and Humphrey Bogart were overseas entertaining the troops. Rick was played on radio by Alan Ladd.
Producer Hal B. Wallis nearly made the character Sam a female. Hazel Scott, Lena Horne, and Ella Fitzgerald were considered for the role.
Renault tells Rick he knows that he ran guns to Ethiopia, referring to Italy's invasion in 1935. In the Italian version of the picture, Renault's line became, "You ran guns to China."
Reportedly, many of the shadows were painted onto the set.