The movie is based on the events surrounding the assassination of democratic Greek politician Grigoris Lambrakis. On May 22, 1963, Lambrakis was attacked and struck on the head (in the same manner depicted in the film) by right-wing extremists after giving an anti-war speech in Thessaloniki. He died of brain injuries from the attack on May 27, 1963. Following Lambrakis's assassination, a military junta of right-wing generals seized control of the Greek government in 1967. During this time, the letter Z (meaning "He is alive") became a common piece of protest graffiti in Greek cities, in memory of Lambrakis and his democratic ideals. The military junta banned the use of the letter "Z" as graffiti, in response to these protests. The Greek junta collapsed in 1974, following a disastrous invasion of Cyprus by Turkey (which led to the occupation of almost half Cyprus by the Turkish army), and democracy was restored to Greece. In the film, the Examining Magistrate (played by Jean-Louis Trintignant) is in reality Christos Sartzetakis, who later served as President of the Hellenic Republic (1985-1990).
Tied with the Fritz Lang movie M (1931) for the record for shortest movie title ever. This happens only in English countries because around the world it is known as the only shortest title of a movie mainly because 'M', in many other countries was released with the subtitle of 'The Vampire of Dusseldorf', while 'Z' didn't receive any kind of subtitles. Holds the record for the movie with the shortest title to be nominated for the Academy Award for Best Picture.
The actor playing the doctor got cold feet during his explanation of the x-rays of Z's cranium. A real doctor acting as an extra, volunteered to fill in and finished the scene, his only acting performance on film.
The producers of the film refused the Golden Globe award given for Best Foreign Language Film because they expected to receive a nomination as Best Motion Picture - Drama. As of 2014, it remains the only film to do so. (Source: Hollywood Foreign Press Association).
At the end of the film there is a list of names banned by the military junta. The names are separated by commas, except for one: "Lurçat !!?!". This is a reference to Jean Lurçat, who was the key figure in the revival of woven tapestry in the 20th century.
The photojournalist played by Actor Jacques Perrin is actually an amalgam of five or six real-life reporters. The actor also acted as co-producer and was instrumental in having the production shot in Algiers.
In the French dialogue, the acronym CROC is expanded as "Combattants Royalistes de l'Occident Chrétien" ("Royalist Soldiers of the Christian West"). In the English subtitled version, the initials are preserved by changing the expansion to "Christian Royalist Organization against Communism".
The music score heard during the scene in which two men fight on the tricycle carrier platform is the same the audience can have in the movie Le Pacha, just before the armored truck heist sequence. This soundtrack was named Batucala Meurtrière, performed by Michel Colombier and never mentioned anywhere. Only a very close watching of the two films can notice that.
The fighting scene between the two men, on the tricycle carrier platform, is performed under the same soundtrack we have in Georges Lautner's Le Pacha, just before the armored truck heist sequence. The soundtrack is named "Batucada Meurtrière", inspired from Brazilian music, and performed by Michel Colombier. It has never been mentioned anywhere, so only a close attention can notice it.