Despite dealing with the serious issues of rape and racial inequality, the novel is renowned for its warmth and humor. Atticus Finch, the narrator's father, has served as a moral hero for many readers and as a model of integrity for lawyers. The historian Joseph Crespino explains, "In the twentieth century, To Kill a Mockingbird is probably the most widely read book dealing with race in America, and its main character, Atticus Finch, the most enduring fictional image of racial heroism." As a Southern Gothic and Bildungsroman novel, the primary themes of To Kill a Mockingbird involve racial injustice and the destruction of innocence. Scholars have noted that Lee also addresses issues of class, courage, compassion, and gender roles in the Deep South. The book is widely taught in schools in the United States with lessons that emphasize tolerance and decry prejudice. Despite its themes, To Kill a Mockingbird has been subject to campaigns for removal from public classrooms, often challenged for its use of racial epithets. In 2006, British librarians ranked the book ahead of the Bible as one "every adult should read before they die".
Reaction to the novel varied widely upon publication. Despite the number of copies sold and its widespread use in education, literary analysis of it is sparse. Author Mary McDonough Murphy, who collected individual impressions of To Kill a Mockingbird by several authors and public figures, calls the book "an astonishing phenomenon". It was adapted into an Academy Award-winning film in 1962 by director Robert Mulligan, with a screenplay by Horton Foote. Since 1990, a play based on the novel has been performed annually in Harper Lee's hometown.
To Kill a Mockingbird was Lee's only published book until Go Set a Watchman, an earlier draft of To Kill a Mockingbird, was published on July 14, 2015. Lee continued to respond to her work's impact until her death in February 2016, although she had refused any personal publicity for herself or the novel since 1964.
The story, told by the six-year-old Jean Louise Finch, takes place during three years (1933–35) of the Great Depression in the fictional town of Maycomb, Alabama, the seat of Maycomb County. Nicknamed Scout, she lives with her older brother Jeremy, nicknamed Jem, and their widowed father Atticus, a middle-aged lawyer. Jem and Scout befriend a boy named Dill, who visits Maycomb to stay with his aunt each summer. The three children are terrified, yet fascinated by their neighbor, the reclusive Arthur "Boo" Radley. The adults of Maycomb are hesitant to talk about Boo, and few of them have seen him for many years. The children feed one another's imagination with rumors about his appearance and reasons for remaining hidden, and they fantasize about how to get him out of his house. After two summers of friendship with Dill, Scout and Jem find that someone is leaving them small gifts in a tree outside the Radley place. Several times the mysterious Boo makes gestures of affection to the children, but, to their disappointment, he never appears in person.
Judge Taylor appoints Atticus to defend Tom Robinson, a black man who has been accused of raping a young white woman, Mayella Ewell. Although many of Maycomb's citizens disapprove, Atticus agrees to defend Tom to the best of his ability. Other children taunt Jem and Scout for Atticus's actions, calling him a "nigger-lover". Scout is tempted to stand up for her father's honor by fighting, even though he has told her not to. One night, Atticus faces a group of men intent on lynching Tom. This crisis is averted in an unexpected manner: Scout, Jem, and Dill show up, and Scout inadvertently breaks the mob mentality by recognizing and talking to a classmate's father, and the would-be lynchers disperse.
Atticus does not want Jem and Scout to be present at Tom Robinson's trial. No seat is available on the main floor, but the Rev. Sykes invites Jem, Scout, and Dill to watch from the colored balcony. Atticus establishes that Mayella and Bob Ewell are lying. It is revealed that Mayella made sexual advances toward Tom, subsequently resulting in her being beaten by her father. The townspeople refer to the Ewells as "white trash" who are not to be trusted, but the jury convicts Tom regardless. Jem's faith in justice is badly shaken. Atticus is hopeful that he can get the verdict overturned, but Tom is shot and killed while trying to escape from prison.
Despite Tom's conviction, Bob Ewell is humiliated by the events of the trial, Atticus explaining that he "destroyed [Ewell's] last shred of credibility at that trial." Ewell vows revenge, spitting in Atticus' face, trying to break into the judge's house and menacing Tom Robinson's widow. Finally, he attacks Jem and Scout while they are walking home on a dark night after the school Halloween pageant. Jem suffers a broken arm in the struggle, but amid the confusion, someone comes to the children's rescue. The mysterious man carries Jem home, where Scout realizes that he is Boo Radley.
Sheriff Tate arrives and discovers Ewell dead from a knife wound. Atticus believes that Jem was responsible, but Tate is certain it was Boo. The sheriff decides that, to protect Boo's privacy, he will report that Ewell simply fell on his own knife during the attack. Boo asks Scout to walk him home. After she says goodbye to him at his front door, he disappears, never to be seen again by Scout. While standing on the Radley porch, Scout imagines life from Boo's perspective.
When the book was released, reviewers noted that it was divided into two parts, and opinion was mixed about Lee's ability to connect them. The first part of the novel concerns the children's fascination with Boo Radley and their feelings of safety and comfort in the neighborhood. Reviewers were generally charmed by Scout and Jem's observations of their quirky neighbors. One writer was so impressed by Lee's detailed explanations of the people of Maycomb that he categorized the book as Southern romantic regionalism. This sentimentalism can be seen in Lee's representation of the Southern caste system to explain almost every character's behavior in the novel. Scout's Aunt Alexandra attributes Maycomb's inhabitants' faults and advantages to genealogy (families that have gambling streaks and drinking streaks), and the narrator sets the action and characters amid a finely detailed background of the Finch family history and the history of Maycomb. This regionalist theme is further reflected in Mayella Ewell's apparent powerlessness to admit her advances toward Tom Robinson, and Scout's definition of "fine folks" being people with good sense who do the best they can with what they have. The South itself, with its traditions and taboos, seems to drive the plot more than the characters.
The second part of the novel deals with what book reviewer Harding LeMay termed "the spirit-corroding shame of the civilized white Southerner in the treatment of the Negro". In the years following its release, many reviewers considered To Kill a Mockingbird a novel primarily concerned with race relations. Claudia Durst Johnson considers it "reasonable to believe" that the novel was shaped by two events involving racial issues in Alabama: Rosa Parks' refusal to yield her seat on a city bus to a white person, which sparked the Montgomery bus boycott, and the 1956 riots at the University of Alabama after Autherine Lucy and Polly Myers were admitted (Myers eventually withdrew her application and Lucy was expelled, but reinstated in 1980). In writing about the historical context of the novel's construction, two other literary scholars remark: "To Kill a Mockingbird was written and published amidst the most significant and conflict-ridden social change in the South since the Civil War and Reconstruction. Inevitably, despite its mid-1930s setting, the story told from the perspective of the 1950s voices the conflicts, tensions, and fears induced by this transition."
Scholar Patrick Chura, who suggests Emmett Till was a model for Tom Robinson, enumerates the injustices endured by the fictional Tom that Till also faced. Chura notes the icon of the black rapist causing harm to the representation of the "mythologized vulnerable and sacred Southern womanhood". Any transgressions by black males that merely hinted at sexual contact with white females during the time the novel was set often resulted in a punishment of death for the accused. Tom Robinson's trial was juried by poor white farmers who convicted him despite overwhelming evidence of his innocence, as more educated and moderate white townspeople supported the jury's decision. Furthermore, the victim of racial injustice in To Kill a Mockingbird was physically impaired, which made him unable to commit the act he was accused of, but also crippled him in other ways. Roslyn Siegel includes Tom Robinson as an example of the recurring motif among white Southern writers of the black man as "stupid, pathetic, defenseless, and dependent upon the fair dealing of the whites, rather than his own intelligence to save him". Although Tom is spared from being lynched, he is killed with excessive violence during an attempted escape from prison, being shot seventeen times.
The theme of racial injustice appears symbolically in the novel as well. For example, Atticus must shoot a rabid dog, even though it is not his job to do so. Carolyn Jones argues that the dog represents prejudice within the town of Maycomb, and Atticus, who waits on a deserted street to shoot the dog, must fight against the town's racism without help from other white citizens. He is also alone when he faces a group intending to lynch Tom Robinson and once more in the courthouse during Tom's trial. Lee even uses dreamlike imagery from the mad dog incident to describe some of the courtroom scenes. Jones writes, "[t]he real mad dog in Maycomb is the racism that denies the humanity of Tom Robinson ... When Atticus makes his summation to the jury, he literally bares himself to the jury's and the town's anger."