What is the theme of "To Kill a Mockingbird"?
As with any literary work with merit, this novel has more than one theme. The main theme is racism and prejudice in our country. This is evident with the entire book centering on the trial of a good man, Tom Robinson, who happens to be black and who also is tried and convicted for a crime he never committed. Had he been a white man, he most certainly would never have been brought to trial in the first place, much less convicted. It is also a novel about social status and economic woes. There are the whites in the community and the blacks in the community of this novel. Mayella Ewell is the alleged victim of Tom Robinson's advances. She is white, but her family is among the lowest on the white totem pole...they live near the black community, but they are considered by everyone in the community to be "white trash". This is mostly (I determine) because it is supposed that Mayella has taken the place of her dead mother in every sense...even with her father's affections. Of course, incest is rarely approved of in any situation. However, they are white, and so therefore, they are situated a notch above the black community. There is also the story of white Mr. Raymond who has a black mistress and children, and who pretends to be the town drunk so that everyone has an excuse to point to for his behavior. The children discover on one afternoon that he really is only drinking cola. There are other themes...keep digging!
The dominant theme in this novel is one of justice, fairness, and the lack thereof in the 1930s south. During this period, segregation and discrimination were rampant, and this novel does not shy away from that fact. What's more, the actions of the characters within this story all have something to do with the idea of equality -- whether it's Atticus's representation of Tom Robinson, Jem's services for Mrs. Dubose, or one of many other scenes in the book, the ideas of fairness are heavily accentuated throughout the plot.
As previously mentioned, this book has a number of different themes. I would recommend that you check services like Sparknotes or Cliffnotes for expanded ideas about this fact.
One of the most powerful themes in the novel is the importance of the experience of learning, the experience of witness, and the realization that independent thinking sometimes requires tremendous courage. Jem and Scout learn that it was wrong to fear Boo Radley. Atticus is witness to the injustice Tom Robinson endures yet does not yeild his beliefs to those who are blinded by hatred and racism. Atticus portrays undeniable courage when he faces the Robinson family...and from the back seat of a car Atticus' child witnesses integrity, descency, and humility. Powerful themes,powerful life lessons.