An epistolary novel is one composed of documents: letters, diary entries, newspaper clippings, telegrams, emails, or any combination of text that a character produces rather than narration that an author imposes from outside. The form dates to the eighteenth century and predates the novel as we know it — Samuel Richardson's Pamela (1740) and Clarissa (1748) established letter-based fiction before the conventions of third-person omniscient narration had solidified. What epistolary form does that no other mode can: it puts the reader in the position of reading over someone's shoulder, seeing only what the character can see, shaped by what the character chooses to say and what they cannot bring themselves to write.
Letters to a Young Poet by Rainer Maria Rilke is the most widely read epistolary text in literary culture — not technically a novel, but a sequence of real letters that reads with the formal completeness of one. Rilke wrote to a young military cadet named Franz Xaver Kappus between 1902 and 1908, and the letters constitute one of the most sustained accounts in the language of what the artistic life requires: solitude, patience with uncertainty, the refusal to seek external validation for an inner necessity. The form matters because it is addressed — Rilke is thinking toward a specific person's situation, not pronouncing from above, and the intimacy of that address gives the advice a weight that more formal essays on the creative life rarely achieve.
Bram Stoker's Dracula (1897) is an epistolary novel that most readers forget is an epistolary novel, because it is too often approached as a horror story rather than as a formal experiment. The entire novel is composed of journal entries, letters, newspaper reports, and a ship's log — and the monster himself never narrates. What makes this formally interesting is that the reader must construct the threat from partial, frightened, inconsistent accounts. No single narrator has the full picture. The horror emerges from gaps between perspectives rather than from direct description, which is precisely what the form enables.
Alice Walker's The Color Purple (1982) uses letters as the only available form for Celie's consciousness. Celie begins writing to God because there is no one else she can tell what is happening to her, and as the novel progresses she begins writing to her sister Nettie in Africa. The letters are the only place where Celie's interior life exists undistorted by the circumstances that have compressed it everywhere else. Walker understood that third-person narration of Celie's situation would impose an observer's distance; letters collapse that distance because Celie is writing directly to the only entities she trusts.
Lionel Shriver's We Need to Talk About Kevin (2003) uses the epistolary form for a different effect: Eva writes to her estranged husband Franklin in long letters about their son Kevin, the cause of the distance between them. The letters are confessional but also evasive — Eva is constructing a version of events that she can live with, which means the reader must read against her narration as much as with it. The epistolary form in Shriver's hands becomes the medium for an unreliable narrator who is not lying exactly, but who is shaping the record. The entire novel is an act of retrospective justification by a woman who needs to understand what she missed.
Helene Hanff's 84 Charing Cross Road (1970) is the other end of the epistolary spectrum from Shriver: a twenty-year correspondence between a New York writer and a London bookseller, built entirely from letters that were not written to be literature. The relationship that develops between Hanff and Frank Doel through the exchange of out-of-print books and, eventually, personal correspondence is one of the most quietly moving in fiction — except it is not fiction. The relationship is real and the form documents it faithfully. This is what letters do at their best: they create a relationship that exists only in writing, and the writing becomes the relationship.
Nick Bantock's Griffin and Sabine series uses the physical properties of letters — you had to open actual envelopes glued to the pages — to create an intimacy that text alone couldn't. More recently, novels like Convenience Store Woman, Jennifer Egan's A Visit from the Goon Squad (which includes a chapter told in PowerPoint), and works composed of emails and texts have expanded what counts as document. The form survives because the underlying principle survives: there is something fiction can do with a character's own words that it cannot do with narration about a character's words. The proximity is formal, not just rhetorical. You are reading the document itself.