Atonement contains elements associated with a number of genres, including historical fiction and psychological fiction. However, it can be argued that the novel's overarching metafictional elements undermine the possibility of neatly classifying it into distinct categories.
The characteristics that give the novel its historical air are rather clear-cut, as the majority of the narrative is set in the years before and during WWII. Through his characters, McEwan offers a 21st-century reader reader insight into how the lives of young people were impacted by the tumultuous 20th century. Rather than seeking to offer the account of a nonfictional event of the past, writers of historical fiction usually devise a fictional plot that is set in a real historical event. This is what McEwan does—the Tallis family is not real, but many of their experiences mirror the real experiences of people who lived during their time. At the same time, McEwan destabilizes this genre classification to a certain degree by muddling the distinction between truth and fiction. In the epilogue, he attempts to dislodge himself from the author role and convince the reader that a character of his creation is the real author. This metafictional move, associated with postmodernism, distinguishes Atonement from more traditional works of historical fiction.
Additionally, the novel can be described as a work of psychological fiction. This is particularly due to McEwan's narrative structure, in which the third-person narrator jumps between the perspectives of a handful of the novel's characters. Inviting the reader into the varying thought patterns of these characters, the narrator's shifting focalization paints a fuller picture of human psychology. The novel stages the immense differences in how people think and behave—and how these differences complicate human relationships. Once again, however, the novel's metafictional elements add further complexity to this genre. When McEwan positions Briony as the novel's real author, he claims that a single character fabricated all of the other characters' psychologies. It is up to the individual reader how different this is from an author who exists outside of a narrative's fictional frame fabricating all of the psychologies within the fictional frame. It is also up to the reader whether this revelation heightens or undermines the novel's classification as psychological fiction.