A trilogy is a set of three works of art that are connected, and that can be seen either as a single work or as three individual works. They are commonly found in literature, film, or video games. Three-part works that are considered components of a larger work also exist in visual arts and music, 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 Godfather films of Francis Ford Coppola, or "The Shiva Trilogy" by Amish Tripathi. Others are connected only by theme: for example, each film of Krzysztof Kieślowski's Three Colors trilogy explores one of the political ideals of the French Republic (liberty, equality, fraternity) and each novel in Paul Auster's The New York Trilogy uses formats from detective fiction to explore existential questions. Trilogies can also be connected in less obvious ways, such as The Nova Trilogy of novels by William S. Burroughs, each written using Brion Gysin's cut-up technique.
Occasionally, the term is applied to music, such as the Berlin Trilogy of David Bowie, linked together by their musical sound and lyrical themes, and the fact that part of them was recorded in Berlin, Germany.
Trilogies — and series in general — are common in science fiction and fantasy.