The Informer is a novel by Irish writer Liam O'Flaherty published in 1925. It received the 1925 James Tait Black Memorial Prize.

Set in 1920's Dublin in the aftermath of the Irish Civil War, the novel centers on Gypo Nolan. Having disclosed the whereabouts of his friend Frankie McPhillip to the police, Gypo finds himself hunted by his revolutionary comrades for this betrayal.

Most famously, the novel was made into a film of the same name by John Ford in 1935 starring Victor McLaglen as Gypo Nolan.

An earlier film adaptation also named The Informer was directed by Arthur Robison in 1929.