Frankenstein; or, The Modern Prometheus is a novel written by English author Mary Shelley (1797–1851) that tells the story of Victor Frankenstein, a young scientist who creates a hideous, sapient creature in an unorthodox scientific experiment. Shelley started writing the story when she was 18, and the first edition of the novel was published anonymously in London on 1 January 1818, when she was 20. Her name first appeared on the second edition, published in 1823.

Shelley travelled through Europe in 1814, journeying along the river Rhine in Germany with a stop in Gernsheim, which is 17 kilometres (11 mi) away from Frankenstein Castle, where, two centuries before, an alchemist was engaged in experiments. Later, she travelled in the region of Geneva (Switzerland)—where much of the story takes place—and the topic of galvanism and occult ideas were themes of conversation among her companions, particularly her lover and future husband, Percy Shelley. Mary, Percy and Lord Byron decided to have a competition to see who could write the best horror story. After thinking for days, Shelley dreamt about a scientist who created life and was horrified by what he had made; her dream later evolved into the novel's story.

Frankenstein is infused with elements of the Gothic novel and the Romantic movement. At the same time, it is an early example of science fiction. Brian Aldiss has argued that it should be considered the first true science fiction story because, in contrast to previous stories with fantastical elements resembling those of later science fiction, the central character "makes a deliberate decision" and "turns to modern experiments in the laboratory" to achieve fantastic results. It has had a considerable influence in literature and popular culture and spawned a complete genre of horror stories, films and plays.

Since the novel's publication, the name "Frankenstein" has often been used to refer to the monster itself. This usage is considered erroneous, but some commentators regard it as well-established and acceptable. In the novel, Frankenstein's creation is identified by words such as "creature", "monster", "daemon", "wretch", "abortion", "fiend" and "it". Speaking to Victor Frankenstein, the monster says "I ought to be thy Adam, but I am rather the fallen angel" (which ties to Lucifer in Paradise Lost, which the monster reads, and which relates to the disobedience of Prometheus in the book's subtitle).