Why is this book famous?

Harper Lee's To Kill A Mockingbird is a literary classic, but it was also a landmark book in the paperback revolution. Thanks to publishers like Penguin Books, paperbacks changed dramatically from pulp fiction and dime store novels to a a legitimate way to read great literature. To Kill A Mockinbird's timing helped it capitalize upon that business shift and become a classic in classrooms — for business reasons as well as literary ones.