What are the main themes?

Harper Lee's great Southern novel, To Kill a Mockingbird, deals with a number of important themes. Among them:

PREJUDICE.  There are many examples of prejudice--racial, gender, social and age among them--in the novel. Perhaps the single most important event is the trial of the Negro Tom Robinson, accused of raping a white women. Attorney Atticus Finch knows beforehand that he cannot possibly gain a jury acquittal due to the racial climate of 1935, in part because no white man will accept the word of a black man over the word of another white man. Tom's innocence is obvious--to everyone but the jury.

TOLERANCE.  Not unlike the prejudices above, the novel is filled with acts of intolerance. Boo Radley is routinely outcast by the entire community because of his unusual nocturnal habits and past troubles. Many of the women, particularly the single ones, are treated as peculiar. Children are held in less regard than in the 21st century, and the social classes are stereotyped. 

LOSS OF INNOCENCE.  The children's loss of innocence is another major theme, since Atticus opens the door for his children to observe the adult world in a manner unusual in small town America in the 1930s. Other characters, such as Boo, Tom and Dill, are also affected.

KNOWLEDGE VS. IGNORANCE.  Intelligent teachers are made to look foolish, and uneducated jurors have the power of life and death in TKAM. Maycomb is a town that is still behind the times, and many of the people are proud of it. Their ignorance of worldly matters is obvious in several chapters.