At Swim-Two-Birds, written by Flann O Brien, also known as Brian O Nolan, and published in 1939, is a highly regarded work in the canon of 20th-century literature. This novel is celebrated for its innovative narrative structure and its playful, metafictional approach to storytelling, making it a seminal work in the postmodern literary movement.

The novel is notable for its unconventional structure: a story within a story within a story. The primary narrative follows an unnamed Irish student who is writing a novel about a man named Dermot Trellis. Trellis, a writer himself, is crafting a story about characters who rebel against him, their creator. This layered narrative allows O Brien to explore the boundaries between fiction and reality, as his characters become aware of their fictional status and interact with both their own world and the world of their author.

O Brien's At Swim-Two-Birds is infused with a rich sense of humour and irony. The novel plays with various genres, including Irish mythology, westerns, and detective stories, weaving them together in a way that both celebrates and satirises traditional narrative forms. Its self-referential nature and the autonomy of its characters have been seen as a precursor to many postmodern literary techniques.

Themes of authorship, literary creation, and the fluid nature of fictional characters are central to the novel. O Brien's work is a testament to the power of imagination and the limitless possibilities of the novel as a form. At Swim-Two-Birds remains a vital and influential work, appreciated for its originality, wit, and its profound commentary on the nature of storytelling.