Prejudice, or holding preconceived opinions of other individuals based not on their merits, but rather other qualities of theirs unrelated to their character, is a main focus of the novel To Kill a Mockingbird. In the novel, Harper Lee explores the question: is it right to look down upon others because of their race, family, religion, or any other similar factors of their lives? The characters of To Kill a Mockingbird represent the victims of prejudice and those who are prejudiced against them. Multiple prejudices exist in daily Maycomb life, often making victims of those who are disadvantaged in Maycomb society.

Racism is the most widespread prejudice in the book, primarily affecting Tom Robinson. Robinson, a black man, was unjustly convicted of a crime just because he was a black man accused by a white man. Atticus addresses the issue when he is discussing the Robinson case with his brother Jack. He describes racism as a disease, saying "Why reasonable people go stark raving mad when anything involving a Negro comes up, is something that I don't pretend to understand..." (93). Atticus succinctly describes the nature of the town's racism; many people of Maycomb will hold biases against a black man before he even speaks, simply because of his race. The blacks being a lower class than the whites is such a widespread belief in Maycomb that blacks live outside the town. One of the only white families living in the same area is the Ewells, whom most people consider "trash," yet all blacks, even those who are honest and hardworking, are placed on the same social level as the worst family in Maycomb. By considering all blacks to be worse than any white man, and shutting them out of the town, the whites of Maycomb show their prejudice against blacks.

Another form of prejudice in Maycomb is the caste system. This sentiment is best embodied in Aunt Alexandra; when she warns Scout not to invite Walter Cunningham home, she argues "You can scrub Walter Cunningham till he shines, you can put him in shoes and a new suit, but he'll never be like Jem. Besides, there's a drinking streak in that family a mile wide"(226-227). Alexandra argues that Scout should avoid socializing with the Cunninghams because of the family they were born into. The caste system in Maycomb is a prime example of prejudice among the populace; just like how many treat blacks as second-class citizens for reasons they cannot control, many people ostracize families they view to be unworthy of being treated decently. Even worse, they justify this prejudice by claiming that the families they dislike have a negative "streak." However, they only believe this because they believe their family is better than others.

Another prejudice common in Maycomb is the prejudice some have against those who hold different religious beliefs than they do. When Aunt Alexandra's invites her missionary circle over for tea, Mrs. Merriweather repeatedly laments the troubles that the Mrunas, an African tribe, face. "You are a fortunate girl. You live in a Christian home with Christian folks in a Christian town. Out there in J. Grimes Everett's land there's nothing but sin and squalor" (234), she says to Scout. Mrs. Merriweather's assumption that a community that is not Christian cannot lead a civilized life is a form of prejudice; she also implies that the reason the Mrunas are in such a bad state is that they are not Christian. Rather than judging the Mrunas on any evil actions they take, she immediately believes them all to be immoral and uncivilized because they do not share her beliefs, even though she has never even met a member of the tribe. This prejudice can also be seen when the foot-washing Baptists insult Miss Maudie for gardening outside. Without having ever had an negative experience with her that could warrant such strong condemnation, they criticize her because she does not follow their beliefs. Many residents of Maycomb assume that those who don't share their beliefs are immoral or uncivilized, a form of prejudice.

These examples and many more represent the prejudice present throughout the entirety of To Kill a Mockingbird. One pattern present in many examples of this is that many of those who perpetuate the prejudice in Maycomb make up negative traits that they then associate with the victims of this prejudice to justify their unreasonable beliefs. For example, many people still claimed that Tom Robinson was guilty of rape, even after it was quite clear that he was not. People were more interested in making sure a black man was not given any more power than they were interested in making sure the courts did not unjustly convict an innocent man. The story of Robinson raping Mayella was simply an excuse for convicting a black man. In a similar fashion, Aunt Alexandra makes up stories about other families being genetically predisposed to have various negative traits, not necessarily because she actually believes it, but because she wants to be able to tell others why the Finches are a superior family. Harper Lee in fact explores the mindset of those who are prejudiced against others in To Kill a Mockingbird.