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, The Apu Trilogy of films by Satyajit Ray, The House of a single anthology stop motion animated film, and The Kingdom Trilogy of television miniseries from 1994 to 2022 by Lars von Trier. Other fiction trilogies are connected only by theme: for example, each film of Krzysztof Kieślowski's Three Colours 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 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—and series in general—are common in speculative fiction.
Trilogies (Greek: τριλογία 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.
Modern fiction trilogies were popularized by the publication of The Lord of the Rings in three volumes for economic reasons (although it was written as a single novel). In addition, 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.
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.
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: the original trilogy, the prequel trilogy released between 1999 and 2005, and the sequel trilogy released between 2015 and 2019.