A trilogy is a set of three works of art that are connected and can be seen either as a single work or as three individual works. They are commonly found in literature, film, and video games, and are less common in other art forms. Three-part works that are considered components of a larger work also exist, such as the triptych or the three-movement sonata, but they are not commonly referred to with the term "trilogy".
Most trilogies are works of fiction involving the same characters or setting, such as The Deptford Trilogy of novels by Robertson Davies and The Apu Trilogy of films by Satyajit Ray. Other fiction trilogies are connected only by theme: for example, each film of Krzysztof Kie?lowski's Three Colors trilogy explores one of the political ideals of the French Republic (liberty, equality, fraternity). Trilogies can also be connected in less obvious ways, such as The Nova Trilogy of novels by William S. Burroughs, each written using cut-up technique.
The term is less often applied to music, such as the Berlin Trilogy of David Bowie which is linked together by musical sound and lyrical themes, all having been recorded at least partly in Berlin, Germany.
The term is seldom applied outside art. One example is the "Marshall Trilogy", a common term for three rulings written by U.S. Supreme Court Chief Justice John Marshall from 1823 to 1832 concerning the legal status of Native Americans under U.S. law.
Trilogies (Greek: trilogia) date back to ancient times. In the Dionysia festivals of ancient Greece, for example, trilogies of plays were performed followed by a fourth satyr play. The Oresteia is the only surviving trilogy of these ancient Greek plays, originally performed at the festival in Athens in 458 BC. The three Theban plays, or Oedipus cycle, by Sophocles, originating in 5th century BC, is not a true example of a trilogy because the plays were written at separate times and with different themes/purposes.
Technical changes in printing and film in the mid-to-late 20th century made the creation of trilogies more feasible, while the development of mass media and modern global distribution networks has made them more likely to be lucrative.
Creators of trilogies may later add more works. In such a case, the original three works may or may not keep the title "trilogy".
The first three novels in The Hitchhiker's Guide to the Galaxy series were dubbed a trilogy, and even after he extended the series, author Douglas Adams continued to use the term for humorous effect - for example, calling Mostly Harmless "the fifth book in the increasingly inaccurately named trilogy."
Kevin Smith's films Clerks, Mallrats and Chasing Amy were often marketed as "The New Jersey Trilogy" because they had overlapping characters, events and locations. After the release of a fourth film, Dogma, the series is referred to as "the View Askewniverse".
The Star Wars Trilogy of three films released between 1977 and 1983 has since been expanded into a trilogy of trilogies, including the original trilogy, the Star Wars Prequel Trilogy released between 1999 and 2005 and the Star Wars Sequel Trilogy released between 2015 and 2019.
Sometimes a trio of works is known as a trilogy because of its creator. Another example of this kind of arrangement is Edgar Wright's Three Flavours Cornetto trilogy, consisting of Shaun of the Dead, Hot Fuzz, and The World's End.
Three works with similar themes from a creator may later come to be known as a trilogy, especially if produced one after the other. An example is the Dollars Trilogy by Sergio Leone; no continuity between the three movies was intended by Leone, but American marketers advertised the Clint Eastwood character in each film as being the same "Man with No Name". Similarly, issues 48, 49, and 50 of the Fantastic Four comic book which introduced the characters of Galactus and Silver Surfer are commonly known as the Galactus Trilogy, although the term wasn't used in the original issues.
In the era of home video, story arcs from a long-running television series might be packaged as a trilogy boxset even if they weren't presented as such originally. The so-called E-Space Trilogy of Doctor Who includes the stories Full Circle, State of Decay and Warriors Gate, consecutive stories set in E-Space.
One of the most popular "trilogies" of fantasy books, The Lord of the Rings by J. R. R. Tolkien, is not a trilogy, though it is often referred to as such. Tolkien regarded it as a single work and divided it into a prologue, six books and six appendices. Because of the high cost of type-setting and the modest anticipated sales, it was originally published in three volumes to minimize any potential financial loss. It is still most commonly sold as three volumes, but has also been published in one-volume and seven-volume editions (six books and the appendices).
Occasionally, more than three works are planned but never finished. The Gormenghast fantasy trilogy is a trilogy by default, as author Mervyn Peake planned to write more novels set in that fictional world until his health declined.