This is a very general question, but I will try to answer it a bit more specifically.
Since To Kill a Mockingbird takes place during the early 1930s during the height of the Great Depression, financial concerns are of importance. Money is scarce, and many of the people of Maycomb are quite poor, though this does not really seem to be of a great concern to Scout, since Atticus (as an attorney) is financially more secure than most.
Racism runs rampant as it would have during this time period in rural Alabama. Jim Crow laws were in effect, and probably a majority of Maycomb's white population considered Negroes as unequal--a second-class race. Atticus is more color blind than most of the people in town, and he is highly respected by Maycomb's black citizens.
Intolerance in other forms, particularly toward gender and mental instability, is also evident, and this is another major theme of the novel.