Why did Harper Lee name the book To Kill a Mockingbird?

The title comes from the idea that some people are targeted unfairly by society because they are different.

When Scout and Jem get guns for Christmas, Atticus tells them not to shoot at mockingbirds.  Unlike some of the other birds he names, he considers Mockingbirds worthy of protection. 

“I’d rather you shot at tin cans in the back yard, but I know you’ll go after birds. Shoot all the bluejays you want, if you can...

The title comes from the idea that some people are targeted unfairly by society because they are different.

When Scout and Jem get guns for Christmas, Atticus tells them not to shoot at mockingbirds.  Unlike some of the other birds he names, he considers Mockingbirds worthy of protection. 

“I’d rather you shot at tin cans in the back yard, but I know you’ll go after birds. Shoot all the bluejays you want, if you can hit ‘em, but remember it’s a sin to kill a mockingbird.” (Ch. 10)

Scout asks Miss Maudie to explain.  She has never heard her father say it’s a sin to do anything before, so he obviously feels very strongly about the mockingbirds.  Miss Maudie tells her that mockingbirds never hurt anyone, and just make music for people to enjoy.

There are two mockingbirds mentioned in the book.  Tom Robinson’s death is compared to “the senseless slaughter of songbirds by hunters and children” by Mr. Underwood in an editorial (Ch. 25).  Boo Radley is the second mockingbird.  When he kills Bob Ewell to protect the children, Atticus and Heck Tate decide not to tell anyone because the notoriety would be a disaster for the shy, reclusive Boo.  Atticus asks Scout if she understands why they are keeping Boo’s involvement a secret.

“Yes sir, I understand,” I reassured him. “Mr. Tate was right.”

Atticus disengaged himself and looked at me. “What do you mean?”

“Well, it’d be sort of like shootin‘ a mockingbird, wouldn’t it?” (Ch. 30)

Boo Radley and Tom Robinson both helped people rather than hurting them, but both were misunderstood.  People were against Tom because he was black and when he was accused of raping a white woman, everyone assumed he was guilty even though all he was doing was helping her.  Boo Radley was a neighborhood recluse who made some bad choices in his youth, and for that the town vilified him.